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FRANKLIN INSTITUTE LIBRARY 


PHILADELPHIA, PA, 


CONCRETE PRACTICE 


BOOKS BY GEORGE A. HOOL 


HOOL—ELEMENTS OF STRUCTURES 
188 pages, 6 X 9, illustrated 


HOOL—REINFORCED CONCRETE CONSTRUCTION 
Volume I—Fundamental Principles 
245 pages, 6 X Q, illustrated 
Volume II—Retaining Walls and Buildings 
666 pages, 6 X 9, illustrated 
Volume IlI—Bridges and Culverts 
688 pages, 6 X 9, illustrated 


HOOL AND WHITNEY—Concretete Drsianers’ MANUAL 
327 pages, 6 X 9, illustrated 


HOOL AND JOHNSON—ConcretTE ENGINEERS’ HAND- 
BOOK 
800 pages, 6 X 9, illustrated 


HOOL AND JOHNSON—Hanppsoox or Buiupine Con- 
STRUCTION 
Two volumes. 1474 pages, 6 X 9, illustrated 


HOOL AND KINNE—Founpations, ABUTMENTS AND 
Foorinaes 
413 pages, 6 X Q, illustrated 


HOOL’ AND KINNE—Structurat MEMBERS AND Con- 
NECTIONS 
611 pages, 6 X 9, illustrated 


HOOL AND KINNE-—Srresses IN FRAMED STRUCTURES 
620 pages, 6 X 9, illustrated 


HOOL AND KINNE—STEeEEL Aanp TIMBER STRUCTURES 
695 pages, 6 X 9, illustrated 


HOOL AND KINNE—ReEtnrorcep CoNcRETE AND Ma- 
SONRY STRUCTURES 
722 pages, 6 X 9, illustrated 


HOOL AND KINNE—Movas.e anp Lona-sepan STEEL 
BRIDGES 
450 pages, 6 X 9, illustrated 


HOOL AND PULVER—Concrete PRAcTICcE 


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(a901d s1.4U0LJ) 


CONCRETE PRACTICE 


A TEXTBOOK FOR VOCATIONAL AND 
TRADE SCHOOLS 


BY 
GEORGE A. HOOL, 8.B. 


Professor of Structural Engineering, The University of Wisconsin 
University Extension Division 


AND 


HARRY E. PULVER, B.S., C.E. 


Associate Professor of Structural Engineering, The University of Wisconsin 
University Extension Division 


First EpIrion 


McGRAW-HILL BOOK COMPANY, Inc. 


NEW YORK: 370 SEVENTH AVENUE 
LONDON: 6 & 8 BOUVERIE ST., E. C. 4 
1926 


CONS 
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726 


CopyRiGuT, 1926, BY THE 
McGraw-Hitut Book Company, Ino. 


PRINTED IN THE UNITED STATES OF AMERICA 


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THE MAPLE PRESS COMPANY, YORK, PA. 


PREFACE 


The authors have attempted to present in this book such 
material as will be suitable to the needs of students in vocational 
courses and it is hoped that this material will also be of value to 
many men engaged in concrete work. 

Attention is called to the exercises and problems accompanying 
practically all of the jobs throughout the text. It is thought that 
these will be of assistance in teaching the subjects treated in this 
book. 

Laboratory and field equipment and the time available will 
usually not permit all of the jobs in the text to be assigned the 
student. The authors have included a large variety of jobs so 
that the instructor can select and use those which will be suitable. 

G. A. Hoot. 
H. E. PULveEr. 


Mapison, WISCONSIN 
November, 1926. 


189990 


vil 


CONTENTS 


PREPAC GAS cla 
Section I. FUNDAMENTAL CONSIDERATIONS 


Composition and Knowledge of Concrete . 
Cementing Materials. ...... 
Portland Cement. ae Me gare 
Manufacture of Portland Gren parte Noe; 
Properties of Portland Cement. eet, 
Portland, Cement Mortars ........ 
Fine Aggregates . 

Coarse Aggregates . i Ae 

Water for Concrete Mixes... . 
Properties of Concrete. A 

Effects of Various Substances on Copcrate. 


Section IJ. Prororrionine, Mrxina, AND PLaciIna CONCRETE 


Job 1. General Theory of Concrete Proportioning ..... . teeny 

Job 2. Proportioning Concrete by Arbitrary Proportions ..... . 

Job 3. Proportioning Concrete with Reference to Voids. 

Job 4. Proportioning Concrete by Sieve Analyses of the Angregstes 
and the Maximum Density Curve. Ai NaN es 

. Proportioning Concrete by the Surface Area Method. ; 

. Proportioning Concrete by the Use of the Tables in the 1924 

Report of the Joint Committee ...... 

Job 7. Proportioning Concrete by the Water-cement Hatio | Sian 
Test. : 

Job 8. Proportioning Coitarets iss a W avercemenré Hato. ‘Slump: 
and Fineness Modulus of Aggregate... .... 

Job 9. Illustrative Example of Proportioning Concrete by che Water, 
cement Ratio, Slump, and Fineness Modulus of Aggregate . 

Job 10. Consistency of Concrete ..... 

Job 11. Measuring Concrete Materials . cee BSS dX 

Job 12. Computing Quantities of Materials for Concrete 2 ont Os 

Joo 1a, tana) Mixing of Conerete...°.. .. .. Sh AAS eto tea! 

Job 14. Machine Mixing of Concrete .... . 

Job 15. Concreting Plant... ; : 

Job 16. Transportation of Concrete. . Nak etek seis 

Job 17, Depositing Concrete in Forms. ....... 

ix 


Job 
Job 


o> 1 


43 


Job 52. 
: Job 53. 


CONTENTS 


. Bonding New Concrete to Old . <a 
. Protection of Concrete when Hardening... . 
. Placing Concrete Under Water .. . . 

. Concreting during Freezing Weather. 

. Making Waterproof Concrete by Proper Prosoricniae a the 


Concrete Materials . 


. Waterproofing Concrete by Adding Integral Compania 
. Waterproofing Concrete by Maes Coatings or Mem- 


branes. 


. Wooden Forms tc Conant eg 
. Types of Wooden Forms for Conccen .'*< eer 
Metal POBpnis. cs sSis ce 

. Removal of Form Marks and ‘Mechanen! Sareice Reeve 
. Use of Colored Aggregates and Pigments. . . 

. Preparation of Wearing Surfaces. ....... 

. Concrete Building Units . eee 

. Concrete Trim and Ornamental Bianes Linge ee 


Section III. Contracts, SPECIFICATIQNS AND PLANS 


. Contracts. : ee 
. Standard Bridge Controns te 

. Specifications. . . . 

. Standard Brcoitiea tone Rl: a  Reinforosa Conctee: Highway 


Bridge. 


el dbs tes CM 
. Standard Plans a a titenirorcea Conerere Highway Bridge 
. Plan Reading. , 


Section IV. EstTimMaTiInG 


. Estimating in General ...... . 

. Estimating Excavation. 

. Estimating Forms. 

. Estimating Concrete. Mga 

. Estimating Stecl for Reinforcement ewe er. 

. Estimating Finishing of Concrete Surfaces... . 

. Estimating Miscellaneous Items. ... . 
. Square and Cube Methods of Estimating Building Goats: 
. Sample Quantity Estimate of Concrete Work. nae 
. Sample Cost Estimate of Concrete Work. ... ... . 

. Time and Work Schedules for Concrete Jobs... . . 

. Progress Reports and Charts ...... 


Section V. Lasoratory METHODS 
Work in the Laboratory . 
Laboratory Reports . 
Inspection and Sampling of Portal Combats 
Normal Consistency of Portland Cement. 


Job 54. 
Job 55. 
Job 56. 
Job 57. 
Job 58. 
Job 59. 
Job 60. 
Job 61. 
Job 62. 
Job 63. 
Job 64. 
Job 65. 
Job 66. 


Job 67. 
Job 68. 
Job 69. 
Job 70. 


Job 71. 


fob 72. 


Job 73. 


Job 74. 


Job 75. 


Job 76. 
Job 77. 
Job 78. 


Job 79. 
Job 80. 
Job 81. 
Job 82. 
Job 83. 
Job 84. 
Job 85. 
Job 86. 


CONTENTS 


Time of Setting of Portland Cement. . 

Soundness Test of Portland Cement. 

Standard Tension Test. 

Fineness 01 Portland Cement... ...... ths 
Inspection and Sampling of Aggregates. . . .. . 
Unit Weight of Concrete Aggregates. . 

Sieve Analyses of Aggregates ....... 

Sieve Analysis Curves ....... : 

Voids in Fine and Coarse Aggregates. 


Silt in Fine Aggregate ...... 


Colorimetric Test of a Fine A oprerates 
Bulking Effect of Water in Sand. 


Tensile Strength of Cement Mortars Made fine Difterent 

. 196 
Tensile Strength of cans Mortars af Diferent Proportions 4 
. 198 


Santis, fore 


Consistency of Portland Cement Concrete 
Proportioning Concrete by Arbitrary Proportions . . 


Proportioning Concrete by the Use of the Tables of the 1924 


Joint Committee Report. 


Proportioning Concrete by the Wintervenent Ratio afd SrinD 


Test. 


Proportioning Conorete bg ae Wa lerecmen ate ‘stump, 


and Fineness Modulus of Aggregate ....... 


Effect of Varying the Amount of Mixing Water in a ‘Given 


Leo 8 ie sae 


Effect of Varying the Rineroes ‘Modulus ai the Kererue: on 


the Economy of the Mix. 


Effect of Varying the Fineness Modulus of the pereoate upon 
the Slump, and upon the Water-cement Ratio Required 

. . 208 

. 211 


fora Given Slump. .... 


Effect of Age on the Compressive Strength ok Generate 


Tests Required for Concrete Materials. 


Testing Machines Used in Testing Concrete ants Golicrern 
. 213 


Materials. ..... : 


Section VI. Freup WorK 


Inspection of Concrete Work ........ 
Supervision of Concrete Work. ........ 
Concrete Basement—Staking Out. 

Concrete Basement—KEstimating . 

Concrete Basement—Excavation . 

Concrete Basement—Forming. ....... 
Concrete Basement—Concreting. ....... 
Concrete Basement—Removal of Forms ....... 


Concrete Sidewalks—Specifications and Estimates. . . . 
Concrete Sidewalks—Location, Grade, Base, and Forms . . 


x1 


Pacr 


. 185 


186 


. 186 
. 187 
. 188 
. 189 
mio 
e LOL 
Lon 
¥ 193 
. 194 


195 


196 


199 


200 


202 


204 


205 


207 


212 


. 218 
. 220 
. 223 
. 225 
Re | 
. 229 
. 231 
. 232 
. 233 
. 234 


CONCRETE PRACTICE 


SECTION I 


FUNDAMENTAL CONSIDERATIONS 


COMPOSITION AND KNOWLEDGE OF CONCRETE 


Concrete is an artificial stone made by mixing, in the proper 
proportions, cement, water, and an aggregate consisting of large 
and small particles. 

The cement, which is the binding material in the concrete, 
should preferably be a portland cement that has passed the stand- 
ard specifications and tests (Appendix 1). 

The water should be clean and free from any impurities which 
would be injurious to the concrete. 

The aggregates are the inert materials in the concrete, such as 
broken stone, gravel, sand, cinders, screenings, etc. There are 
_ two classes of aggregates, fine and coarse. A fine aggregate is 
usually defined as the material passing a No. 4 sieve, and a coarse 
aggregate as the material held on (not passing) a No. 4 sieve. 
This sieve is one having four meshes per lineal inch. The aggre- 
gates should be of such materials, sizes, and grading as will be 
suitable for the concrete work contemplated. 

To obtain quality concrete, it is necessary to use good materials, 
to have the concrete mix correctly proportioned, the batch thor- 
oughly mixed and carefully placed in the forms, and then the 
concrete allowed to harden under suitable curing conditions. 

It is evident that a comparatively extensive knowledge is 
required, based on study and experience, before good concrete can 
be made consistently. A vast fund of information concerning 
concrete and concrete materials has been obtained, and made 
available for use through the efforts of cement manufacturers, 

1 


2 CONCRETE PRACTICE 


various associations and societies (especially the Portland Cement 
Association and the American Concrete Institute), testing labora- 
tories, and a large number of consulting engineers. The concrete 
industry, however, even considering the large amount of concrete 
now made each year, is yet in its infancy, and many facts con- 
cerning concrete are still undiscovered. . 


CEMENTING MATERIALS 


Cementing materials may be classified as follows: 


Non-hydraulie: Hydraulic: 
Gypsum plasters Hydraulic lime 
Common lime Puzzolan or slag cement 


Natural cement 
Portland cement 
Quick-hardening cements 


Hydraulic cements will set under water, which is not true of 
non-hydraulic cements. 

Gypsum plasters are produced by the partial or complete 
dehydration (dewatering) of gypsum. Plaster of Paris is a 
partially dehydrated gypsum. 

Common lime is made by burning a comparatively pure lime- 
stone at alow temperature. It will slake when mixed with water, 
but will not set under water. 

Hydraulic lime is made by burning a slightly argillaceous lime- 
stone at a low temperature. It will slake slowly, and will set 
very slowly under water. 

Puzzolanic or slag cement is made by mixing slaked lime with 
natural puzzolanic materials, or with granulated blast-furnace 
slag. This cement will not slake, but it has hydraulic properike : 
when ground. 

Natural cement is made by burning an argillaceous lirnegeare 
(limestone containing clay) at a comparatively high temperature. 
It will not slake, but, when ground, has hydraulic properties. 

Portland cement is made by burning an artificial mixture of 
argillaceous and calcareous materials to the high temperature of 
incipient fusion, and then finely grinding the clinker. Portland 
cement will not slake, but it has very marked hydraulic properties 
when finely ground. 


FUNDAMENTAL CONSIDERATIONS 5) 


Most of the so-called quick-hardening cements are made in about 
the same manner as portland cement, except that different propor- 
tions and kinds of raw materials are used. These cements, in gen- 
eral, are very similar to portland cement in their properties, except 
that they will harden and obtain their strength much more rapidly. 


PORTLAND CEMENT 

Portland cement, the most important of all of the cementing 
materials at the present time, is defined as the product obtained 
by finely pulverizing clinker, produced by calcining to incipient 
fusion an intimate and properly proportioned mixture of argilla- 
ceous and calcareous materials, with no additions subsequent to 
calcination excepting water and calcined or uncalcined gypsum. 

The principles of making a hydraulic cement were discovered in 
the year 1756, by John Smeaton of England, but he did not carry 
his investigations far enough, and it was left for another man 
really to start the portland cement industry. This man was 
Joseph Aspdin, a bricklayer in the town of Leeds, England. As 
a result of his experiments, Mr. Aspdin was able, in the latter 
part of 1824, to obtain a patent for a superior kind of cement. 
This cement he called ‘‘portland”’ cement, because of its resem- 
blance to the building stone obtained from the island of Portland. 

Joseph Aspdin erected his first portland cement plant in Wake- 
field, and, after overcoming many difficulties, was able to produce 
his cement on a commercial scale. He was assisted in his work 
by his sons, William and James. William Aspdin made several 
improvements in the process of manufacture, and later, in 1854, 
went to Germany and established three plants in that country. 

During the period 1840 to 1860 several other portland cement 
plants were started, and the new industry had a slow but sure 
growth. This slow growth was due mainly to the increasing use 
of Roman cement, a natural cement invented by James Parker, in 
1791. It was not until about 1865, that portland cement super- 
seded its rival, Roman cement, in the construction field in 
England. 

In later years, the invention and periection of rotary kilns, ball 
and tube mills, and other machinery did much to improve the 
quality of the cement and to reduce the cost of manufacture. 

Although natural cement was first manufactured in the United 
States in about 1820, it was not until 1872 that David O. Saylor 


4 CONCRETE PRACTICE 


began his investigations with portland cement. From that time 
until about 1900, the growth of the portland cement industry in 
the United States was comparatively slow. Even as late as 
1894, there were only about twenty portland cement plants in this 
country, producing about 800,000 bbl. of cement annually, while 
the annual production of natural cement at that time was about 
8,000,000 bbl. 

Since about 1900, further discoveries of suitable raw materials 
throughout the country, improvements in manufacturing machin- 
ery and processes, and the resultant reductions in costs have 
tended rapidly to increase the use of portland cement so that the 
United States now surpasses the rest of the world in the produc- 
tion and use of this material. 

Today, the American portland cement industry has about 140 
plants employing approximately 40,000 men, and producing 
about 150,000,000 bbl. of cement annually. Portland cement 
of good quality is now available in all parts of this country at 
fairly reasonable prices. 

The wonderful growth of the portland cement industry has 
been mostly due to the systematic development and improvement 
of efficient grinding machinery, rotary kilns, chemical control — 
during manufacture, standard specifications, and the various 
uses of portland cement. 

Portland cement now ranks next to steel and timber as a 
structural material, and it may outrank timber in the near future. 


MANUFACTURE OF PORTLAND CEMENT 


The raw materials generally used in the manufacture of port- 
land cement are those listed in the following table: 


Raw MarTeEerRIALs FOR PoRTLAND CEMENT MANUFACTURE 


Argillaceous materials Calcareous materials 
Argillaceous limestone Pure limestone 

Clay or shale Pure limestone 

Clay or shale Marl 

Blast furnace slag _ Pure limestone 


Clay or shale Chalk or chalky limestone 
Clay or shale Alkali waste ' 


FUNDAMENTAL CONSIDERATIONS 5 


Many of these materials are obtained by quarrying, after which 
they are conveyed to powerful crushers, and broken up into small 
sizes suitable for the grinders. In the dry process, the crushed 
materials are dried, mixed in the correct proportions, and then 
ground in mills to a powder, so that about 95 per cent of the 
materials will pass a 100-mesh sieve. These finely ground mate- 
rials pass into a large rotary kiln, where they are burned to a 
clinker at a maximum temperature of about 3000°F. After the 
clinker has been sprayed with water and cooled, aretarder (usually 
gypsum) is added, and the material is then finely ground in mills, 
so that 78 per cent or more will pass a standard 200-mesh sieve. 
The cement is now conveyed to a storage bin for seasoning. 

In the wet process of manufacture, the materials are usually 
ground when wet, after which they are mixed in the correct 
proportions and enough water added to make a thin mud or 
slurry. The mixing isdoneina pugmill. This slurry is pumped 
to a vat, where a chemical analysis is made, and the proportions 
- corrected when necessary. From the vats, the slurry is conveyed 
to a special type of rotary kiln in which it is burned. 

After the clinker is removed from the kiln, the remaining part 
of the wet process of manufacture is similar to that of the dry 
process. | 

The wet process permits of better chemical control and easier 
grinding than the dry process does, but requires a little more fuel 
for burning. 

After being seasoned in storage bins for a few weeks, the cement 
is usually packed in sacks holding 94 lb., or in barrels holding 376 
Ib., and made ready for shipment. Sometimes the cement is 
shipped by bulk in railway cars. 

When portland cement is stored under ordinary conditions, it is 
apt to deteriorate. Consequently, cement that has been stored 
for more than a few weeks should be retested before being used in 
important concrete work. If, however, the cement is stored so 
that it is protected from moisture and carbon dioxide in the air, 
it may be kept indefinitely without loss of strength. 


PROPERTIES OF PORTLAND CEMENT 


Portland cement is a valuable structural material, because it 
has strength and soundness after hardening. In order to com- 


6 CONCRETE PRACTICE 


pare different portland cements as to their qualities, and to 
determine their suitability for use, it is necessary to make certain 
standardized tests on the cements, and to observe if they pass 
certain standard specifications. (See Appendix 1 for the Stand- 
ard Specifications and Tests for Portland Cement.) 

The most important quality of portland cement is soundness. 
It is not desirable to use a cement for structural purposes, if that 
cement will later disintegrate and crumble and cause a failure of 
the structure. Unsoundness is usually shown by expansion after 
the cement has set, followed by disintegration. Free lime in the 
cement is the most common cause of unsoundness. The steam 
test (accelerated test) is valuable for determining the soundness of 
a portland cement. 

The next quality, in order of structural importance, is strength. 
The compressive strength of a cement, when made into a mortar 
or a concrete, is the best criterion to use, but, because the tensile 
test was easier to standardize and apply, the tensile strength of a 
1:3 mortar, made of a portland cement and the standard Ottawa 
sand, has been selected as a means of comparing different port- 
land cements and also for determining their suitability for use. 
The tensile strength of neat portland cement is about 600 lb. per 
sq. In., or more, at an age of 28 days, while the neat compres- 
sive strength isabout ten times this value. ‘Theshearing strength 
is about the same as the tensile strength. Finer grinding of the 
cement will increase the strength of the mortar, but not of the 
neat cement. 

The time of set is important, in that the cement should obtain 
its initial set slowly enough so that there will be ample time first 
to place the mortar or concrete in the forms. ‘Too long a time 
should not be required for the hard set, or the progress of the work 
may be delayed. In general, warm or dry weather will shorten 
the time required for setting, while an excess of water will 
lengthen it. An addition of gypsum or plaster of Paris up to 
about 3 per cent by weight will retard the time of set, while a 
larger addition of plaster of Paris may give the cement a ‘‘flash”’ 
set. 

Fineness of grinding is important, as the finer particles of the 
cement determine its cementing values. Fine grinding increases 
the strength of cement mortars, increases the sand-carrying 


FUNDAMENTAL CONSIDERATIONS ri 


capacity, decreases the time of set, and seems to make the cement 
more sound. 

The test for specific gravity is usually not made unless specifi- 
cally ordered. This test ig sometimes useful for determining 
possible adulterations of the cement. 

The specifications require, in regard to the chemical properties 
of portland cement, that certain limits be not exceeded. Chemi- 
cal tests are not often made on a commercial sample, unless this 
sample should fail to pass the physical tests. 


Ezxercises—What are the specification limits for tensile strength? For 
time of set? For fineness? 

Would a portland cement be considered suitable for use in concrete work, 
if the test results were as follows: 

Chemical properties—satisfactory. 

Specific gravity—3.12. 

Percentage passing the standard 200-mesh sieve—79 per cent. 

Soundness—pat remained hard and firm and showed no signs of distortion, 
checking, cracking, or disintegration. 

Tensile strength of 1:3 standard sand mortar—at 7 days = 328 lb. per 
sq. in.; and at 28 days = 316 lb. per sq. in. 


PORTLAND CEMENT MORTARS 


A portland cement mortar is a mixture of portland cement, 
water, and a fine aggregate (sand or its equivalent). The port- 
land cement should be one capable of passing the standard 
specifications (Appendix 1). The water should be clean and free 
from any impurities which would be injurious to the mortar. 
The requirements for fine aggregate are given in the next article. 

The mortar may be proportioned by weight or by volume. 
Proportioning by weight is the better method, and is used toa 
large extent in laboratories, while proportioning by volume is 
generally used on the job. If the sand is wet, the proportions 
should be corrected for the water present. When measuring wet 
sand by volume, the bulking effect of the water may be quite 
large, and this effect should be determined and allowance made. 

The mortar may be mixed either by hand or by machine. 
Machine mixing is faster, and the quality is more uniform than in 
hand mixing. The batches should not be too large. The cement 
and sand should be mixed dry, the water added, and the batch 
mixed again. Thorough mixing is essential. 


8 CONCRETE PRACTICE 


The mortar should be used before the initial set has occurred. 
Retempering (remixing) of a portland cement mortar should not 
be permitted after the initial set has taken place. 

In general, the strength of a portland cement mortar depends 
upon the proportion of the cement, the amount of the mixing 
water, and the size and grading of the sand. Other things being 
equal, increasing the proportion of cement increases the strength, 
while increasing the amount of water decreases the strength and 
lengthens the time of set. Just sufficient water should be used to | 
give a workable mix. In regard to the sand, test results show 
that the densest sand usually makes the strongest mortar, that 
the proportion of fine sand should be small, and that coarse sand 
makes a stronger mortar than fine sand. 

The tensile strength of a 1:3 mortar made with a good sand 
should be equal to, or more than, 200 lb. per sq. in. at an age of 7 
days, and equal to, or more than, 300 lb. per sq. in. at an age 
of 28 days. 

The compressive strength of a good 1:3 mortar should be 1200 
lb. per sq. in. or more at an age of 7 days, and 2000 lb. per sq. in. 
or more at an age of 28 days. 

The transverse (cross-bending) strength is approximately 
twice the tensile strength. 

The adhesive strength depends upon the materials to which the 
mortar is attached, but is never more than the tensile strength of 
the mortar. 

The weight of a good portland cement mortar of a 1:1 mix is 
about 145 lb. per cu. ft.; of a 1:3 mix about 140 lb. per cu. ft.; 
and of a 1:4 mix about 138 lb. per cu. ft. 


Exercises —Which method of proportioning mortar is the better? Why? 
What is the effect of using too much mixing water? 
On what does the strength of a portland cement mortar depend? 


FINE AGGREGATES 


Sand of some kind is found in practically every locality of the 
United States. Most of the sands are suitable for use in concrete, 
especially after they have been washed to remove clay and dirt, 
and have been screened to remove particles that are too large. 
Sometimes a sand is found that is not suitable for use in concrete, 


FUNDAMENTAL CONSIDERATIONS 0 


in which case another sand should be procured, even if it must be 
shipped in from some other locality. 

Visual inspection of a source of supply is an aid in determining 
the qualities of a sand. The mineral constituents may be 
identified, the uniformity of supply and of grading approximately 
determined, and the presence of silt (either free or adhering to the 
grains) may be noted. A rough test for the presence of silt may be 
made by rubbing a small amount of the sand in the palm of the 
hand, and observing if the palm is stained. A stain denotes the 
presence of silt. 

The best sand for concrete work, as to grading, is one which 
contains both coarse and fine grains in such proportions that the 
percentage of voids will be a minimum. A coarse-grained sand 
is better than a fine-grained one. Impurities, such as those 
mentioned in the specifications which follow, should not be pres- 
ent, as they may make the sand worthless for concrete purposes. 
A small percentage of finely divided clay or loam is not usually 
injurious. | 

The percentage of voids in a sand usually ranges from 25 to 45 
per cent. The weight per cubic foot varies from about 85 to 120 
Ib. for dry sands tested according to the method in Appendix 2. 
The weight per cubic foot of loose sand may be as much as 20 
per cent less than that of the same sand compacted by rodding. 
Moist sand weighs less than dry sand. The percentage of absorp- 
tion of a sand rarely exceeds 3 per cent. The specific gravity of 
sand usually varies from 2.6 to 2.7 with an average value of 2.65. 
_ The bulking effect of water in sand should be allowed for when 

measuring wet sand by volume. When water is added to a sand, 
it wets the surface of the grains, forming a film of water around 
each particle, as well as tending to fill the voids. This surface 
film forces the grains of sand apart and causes bulking, the 
amount of the bulking depending upon the amount of water 
_ present and the fineness of the sand. The bulking effect increases 
with the surface area of the sand. The maximum bulking effect 
usually occurs with about 5 or 6 per cent of water by weight. 
The maximum amount of bulking varies with different sands; 
in fine sand it may be as great as 30 per cent; in medium sand, 25 
per cent; and in coarse sand, 20 per cent. The addition of from 
1 to 2 per cent of water by weight may increase the volume from 


10 CONCRETE PRACTICE 


10 to 20 per cent in some instances. When from 16 to 20 per 
cent of water is added, the sand becomes completely flooded or 
inundated, and its volume becomes nearly the same (often a few 
per cent more) as that of the dry sand. The inundating of a sand 
overcomes the bulking effect and, when a sand is measured in a 
completely immersed condition, its volume is practically the same 
as that of the same sand in a dry condition. These values are 
for a sand which has been fairly well tamped. The bulking 
effect on a loose sand would probably be from 30 to 50 per cent 
more than the values given. 

The sieve analysis test of a sand, as described in Appendix 3, is 
one of the best tests for determining the suitability of the sand as 


ee 
Ss 
S 


Percentage Fassing Sieve 


0 0025 0050 0075 0100 Ql25 0150 175 0200 0225 0250 
Diameter of Particle in inches 


Fig. 1.— Typical mechanical analyses of fine, medium, and coarse sands. 


a concrete aggregate. The results of a sieve analysis may be 
plotted as in Fig. 1, and the comparative grading determined at 
a glance. This figure shows typical sieve analysis curves for 
fine, medium, and coarse sands. 

The fineness modulus for a fine aggregate is equal to one-one 
hundredth of the sum of the percentages by weight of this aggre- 
gate retained on (coarser than) the following standard square mesh 
sieves: Nos. 4, 8, 16, 30, 50, and 100. The 3¢-in. sieve should be 
included when sieving coarse sands. (Refer to Appendix 3 for 
sizes of sleve openings and wire diameters.) A fine aggregate, 
having a fineness modulus of from about 2 to 3.60, is considered 
suitable for concrete work. | 

For a description of the standard Ottawa sand used in the 
testing of portland cement, see Sec. 50 of Appendix 1. The 


FUNDAMENTAL CONSIDERATIONS jt 


percentage of voids in this sand is about 37 and the weight per 
cubic foot is about 104 lb. 

Stone screenings, the fine material that has been screened out of 
crushed stone, may be a good, fine aggregate for concrete, when 
free from clay and dirt. ‘Stone screenings may be a little coarser 
than an average sand, but they have about the same percentage 
of voids and weight per cubic foot. 

The following specifications for fine aggregate for concrete are 
taken almost verbatim from the 1924 Report of the Joint Commit- 
tee on Standard Specifications for Concrete and Reinforced 
Concrete. 


Specifications for Fine Aggregate for Concrete.—Fine aggregate for con- 
crete shall consist of sand or other approved inert materials of similar charac- 
teristics, or a combination thereof, having clean, hard, strong, durable, 
uncoated grains, and free from injurious amounts of dust, lumps, soft or 
flaky particles, shale, alkali, organic matter, loam, or other deleterious 
substances. 

The fine aggregate shall range in size from fine to coarse particles within 
the limits given in the following table: 


GRADING OF FinE AGGREGATE 
Per Cent BY WEIGHT 


Paesinw NOLS SIGVE....2.....0... Not less than 85 
Passing No. 50 sieve............. Not more than 30 and not less than 10 


Weight removed by decantation... Not more than 3 


The sieves and method of making sieve analysis shall conform to the 
Standard Method of Test for Sieve Analyses of Aggregates for Concrete 
(Serial Designation: C41—24) of the American Society for Testing Materials 
(Appendix 3). _ 

The decantation test shall be made in accordance with the Tentative 
Method of Decantation Test for Sand and Other Fine Aggregates (Serial 
Designation: D136-22T) of the American Society for Testing Materials 
(Appendix 4). 

Fine aggregate shall be of such quality that mortar briquettes, cylinders, 
or prisms, consisting of one part by weight of portland cement and three parts 
by weight of fine aggregate, mixed and tested in accordance with the methods 
described in the Standard Specifications and Tests for Portland Cement 
(Appendix 1), will show a tensile or compressive strength, at ages of 7 and 
28 days, not less than 100 per cent of that of 1:3 standard Ottawa sand 
mortar of the same plasticity made with the same cement. Concrete tests 
shall be made in accordance with the Standard Methods of Making Com- 
pression Tests of Concrete (Serial Designation: C39-25) of the American 
Society for Testing Materials (Appendix 8). 


12 CONCRETE PRACTICE 


In testing an aggregate, care should be exercised to avoid the removal 
of any coating on the grains which may affect the strength. Sand should 
not be dried before being made into mortar, but should contain its natural 
moisture. The quantity of water contained may be determined on a sepa- 
rate sample, and the weight of the sand in the test corrected accordingly. 

Sand, when tested in accordance with the Standard Method of Test 
for Organic Impurities in Sand for Concrete (Serial Designation: C40—22) 
of the American Society for Testing Materials (Appendix 5), shall show 
a color not darker than the standard color, unless it complies with the 
strength requirements of the preceding paragraphs. 

Fine aggregate, which does not conform to the above requirements for 
grading, mortar strength, or color, may be used only when approved by 
the engineer, and then in such proportions as he may require. 

The test for the unit weight of the fine aggregate shall be made in accord- 
ance with the Standard Method of Test for Unit Weight of Aggregate for 
Concrete (Serial Designation: C29—21) of the American Society for Testing 
Materials (Appendix 2), and the results included with the other test data for 
the fine aggregate. 

Fine aggregate shall be stored so as to avoid the inclusion of foreign mate- 
rials. Frozen aggregate or aggregate containing lumps of frozen material 
shall be thawed before using. 

Exercises.—A sieve test of a sand gave the following results: 


PER CENT 
Passing No. 4 sieve: .......c. 5). 0- 90 100 
Passing No. 50 sieve. .. 2... .. 276) se 34 
Weight. removed by decantation. <..-... .; 22 2.7 


Does this sand pass the specifications for grading and weight removed by 
decantation for fine aggregate for concrete? 
A sieve analysis of a 500-gram sample of a sand gave the following results: 


Passing No. 4 sieve........04. sek ote 486 g. 
Passing No. 8 sieve... :..).5 0 uss ae 420 g. 
Passing No. 16 sieve.?....°...-.3.9.. ee 315 g 
Passing No.. 30 sieve. >... 3... > ss. ee 170 g. 
Passing No. 50 sieve. ..9:........... eee 82 g. 
Passing No. 100 sieve...) .. 2... «a0. 2 4 ee 12'¢. 


Plot a sieve analysis curve for this sand on a sheet of cross-section paper, 
plotting percentages passing as ordinates (vertically) and sieve openings 
as abscissae (horizontally). 

Does this sand pass the specifications for the grading of a fine aggregate 


given in this article? 
Compute the fineness modulus of this sand. 


COARSE AGGREGATES 


The coarse aggregates commonly used in concrete are river and 
bank gravels, crushed limestone, granite, trap rock, blast fur- 


FUNDAMENTAL CONSIDERATIONS 13 


nace slag, and cinders. The gravels frequently contain dirt, silt, 
and sand, and often require washing and screening before being 
usable. In general, a bank-run gravel should not be used in 
concrete unless it has been thoroughly tested and found to be 
satisfactory. It is usually necessary to wash a bank-run gravel 
and then screen out either its fine or its coarse material. When 
available, a good gravel is a very economical coarse aggregate for 
concrete. Crushed limestone, granite, and trap rock are all 
good for a concrete aggregate. A good, crushed-rock concrete is 
frequently a little stronger than a gravel concrete of the same 
proportions. Rocks such as shales, most of the sandstones, and 
very soft limestones are unsuitable as a coarse aggregate. Cin- 
ders of good quality have been used as coarse aggregates where 
light weight rather than strength is desirable. Blast-furnace 
slag, with a low sulphur content, may make an excellent concrete 
aggregate, but, because of its porosity, it should not be used in 
thin sections which may be subjected to water action. 

Visual inspection of a supply of coarse aggregate will give a 
good idea as to the mineral constituents, uniformity of supply, 
and approximate grading of the particular aggregate. The 
presence of dirt, clay and silt in the coarse aggregate may also 
be detected. 

In general, any crushed stone or gravel is suitable for concrete 
work that is durable and strong enough, so that the strength of 
the concrete is not limited by the strength of the aggregate. 
Desirable properties are density, hardness, toughness, strength, 
durability, grading, and cleanliness. The best coarse aggregate 
for concrete work, as to grading, is one that has a comparatively 
large fineness modulus and a small percentage of voids. For 
massive concrete work, the maximum size of the particles may 
be 2.5 or 3 in., while in reinforced concrete work the maximum 
size may be 0.75, 1, or 1.50in. ‘The coarse aggregate must not be 
so large that it will not work freely around the reinforcement and 
into the crevices and corners of the molds and forms without 
extra tamping and rodding. 

Of the igneous rocks, granite and trap are suitable materials 
for coarse aggregate. Of the sedimentary rocks, compact calcium 
and magnesium limestone make excellent coarse aggregates. 
A very soft limestone, or a limestone containing a large percentage 


14 CONCRETE PRACTICE 


of clay, will probably not prove to be a good material for concrete. 
Most of the sandstones do not make good aggregates, because of 
their tendency to disintegrate. Some sandstones, in which the 
cementing material is lime carbonate, have been successfully used 
as coarse aggregates. Gravel which is clean and of a good 
mineral quality is a very satisfactory concrete material. Crushed 
rocks or gravels containing particles of clay, shale, or mica, or 
having thin, elongated, laminated, or friable pieces do not make 
good concrete aggregates. 

The percentage of voids in common crushed stone and gravel 
varies from about 30 to 55 per cent, depending to some extent on 


Fercentage Passing Sieve 


<S 
= 


<< 


450 


_ 050 0.75 100 125 
Diameter of Particle in inches 


Fia. 2.—Typical mechanical analyses of fine, medium, and coarse gravels. 


the shape of the particles, the grading, and the degree of compact- 
ness. The weight per cubic foot of crushed stone and gravel will 
vary from 75 to 120 lb., the gravel usually being a little heavier 
than crushed stone. The weight per cubic foot of cinders is fre- 
quently under 90 lb. 

The specific gravity of stone and gravel varies somewhat. 
Approximate values are as follows: granite from 2.65 to 2.75; trap, 
2.80 to 3; limestone, 2.60 to 2.70; sandstone, 2.30 to 2.60; ordinary 
gravel and sand, from 2.60 to 2.70. The percentage of absorption 
of crushed stone or gravel will usually be from 2 to 4 per cent. 

The bulking effect of water on most crushed stones and gravels 
is inappreciable, and need not be considered when making 
measurements by volume. 


FUNDAMENTAL CONSIDERATIONS 15 


A sieve analysis of coarse aggregate, made as described in 
Appendix 3, is an aid in determining the suitability of coarse 
aggregate for use in concrete mixes. If desired, the results of a 
sieve analysis may be plotted as a curve, as shown in Fig. 2, and 
the comparative grading of the particles shown. Sieve analysis 
curves for coarse aggregates of three different gradings are shown 
in this figure. 

The fineness modulus is one way of measuring the grading of a 
coarse aggregate. The fineness modulus for a coarse aggregate 
may be defined as the sum of the percentages of the sample of 
coarse aggregate retained on (coarser than) the 114-in., 34-in., 
3g-in., and No. 4 sieves plus 500 (for the five smaller sieves), 
and the total divided by 100. A coarse aggregate that is good 
for concrete work will have a fineness modulus of from 6 to 8. 

The following specifications for coarse aggregate are taken 
almost verbatim from the 1924 Report of the Joint Committee on 
Standard Specifications for Concrete and Reinforced Concrete: 


Specifications for Coarse Aggregate for Concrete.—Coarse aggregate 
shall consist of crushed stone, gravel, or other approved inert materials 
with similar characteristics, or combinations thereof, having clean, hard, 
strong, durable, uncoated particles free from injurious amounts of soft, 
friable, thin, elongated, or laminated pieces, alkali, organic, or other deleteri- 
ous materials. 

Coarse aggregates shall range in size according to the limits given in the 
following table: 


S1zE AND GRADING OF COARSE AGGREGATE 


Nominal Percentages by weight passing through __|Percentage pass- 


maximum standard sieves with square openings ing notmorethan 
size of 
aggregate, : : oe . ae fee No. 4 | No. 8 
al Sei ein, (134-1n,) Lin. |'24 im. | 4.1n. ewer ee 
3 95 a BOS ie mee. etre os i 10 5 
2 SEAS pan pa 40-75|...... rf. 10 5 
1% Oval barat ccs .| 40-75]... 10 5 
Pee ss fk ee O54 © Peaks EN 10 5 
A en ee rar .| 95 . 10 5 
1 OT es rr supe Be 95 10 5 


16 CONCRETE PRACTICE 


The test for size and grading of aggregate shall be made in accordance 
with the Standard Method of Test for Sieve Analysis of Aggregates for 
Concrete (Serial Designation: C41—24) of the American Society for Testing 
Materials (Appendix 8). 

Coarse aggregate which does not conform to the above requirements 
may be used only when approved by the engineer, and then in such propor- 
tions as he may require. 

The test for unit weight of coarse aggregate shall be made in accordance 
with the Standard Method of Test for Unit Weight of Aggregate for Con- 
crete (Serial Designation: C29-21) of the American Society for Testing 
Materials (Appendix 2), and the results included with the other test data for 
the coarse aggregate. 

Coarse aggregate shall be so stored as to avoid the inclusion of foreign 
materials. Frozen aggregate or aggregate containing lumps of frozen 
material shall be thawed before using. 

Exercises.—A sieve test of a bank gravel gave the following results: 


Per Cant 
Passing the 114-in. sieve..... .. «.)..as ane oe 96 
Passing the %4-in. sieve. ../.......5.4 7050 67 
Passing the No. 4 sieve........ MP A 12 
Passing the No. 8 sieve... ...... 00. 4.0 foe 9 


Is the grading of this bank gravel satisfactory, if the gravel is to be used for 
concrete work? Why? 
A sieve analysis of a crushed stone gave the following results: 


Sieve size and number..... Loovta. 0.75 in. | 0.375 in. No. 4 
Percentage passing........ 100 69 18 5 


Plot the sieve analysis curve for this crushed stone on a sheet of cross- 
section paper, plotting percentages passing as ordinates and sizes of sieve 
openings as abscissae. 

Does this crushed stone pass the specifications for grading for coarse 
aggregate in this article? 

Compute the fineness modulus of this crushed stone. 


WATER FOR CONCRETE MIXES 


The water used in concrete mixes should be clean and free from 
injurious amounts of oil, acid, alkali, or other deleterious sub- 
stances, and should be of a quality fit for drinking purposes. 

The presence of oil in water is shown by an iridescent surface 
film. Vegetable matter in water can sometimes be detected by 
observing floating particles. Chemical tests should be made to 
determine the presence of organic matter in all doubtful cases. 


FUNDAMENTAL CONSIDERATIONS i 


The acidity or alkalinity of a water may be determined by 
immersing strips of red and blue litmus paper. If the blue strip 
changes quickly to a red color, the water is dangerously aciditic. 
If the red strip changes quickly to a blue color, the water is 
dangerously alkaline. The water is neutral when there are no 
color changes. If the color change is very slow and faint, the 
water may be only slightly aciditic or alkaline, and the indication 
may be disregarded. 

The functions of water in a concrete mix are threefold: 

1. To combine chemically with the cement and give strength 
to the concrete. 

2. To flux the cementing material over the surfaces of the 
particles of the aggregate. 

3. To lubricate the mix so that the concrete may be readily 
placed in the forms. 

Just enough water should be used to give a workable mixture. 
An excess of water: (1) reduces the strength of the concrete; (2) 
occupies space in the concrete, and later causes voids after drying 
out; (3) causes laitance, a whitish deposit on the surface of the 
concrete; (4) causes work planes or planes of separation between 
one day’s work and the next; (5) reduces the water-tightness of 
the concrete; (6) causes poor surfaces next to the forms; (7) 
causes poor concrete floor surfaces, and tends to make the floors 
dusty; (8) tends to prevent the bonding of new to old concrete; 
and (9) increases the risk of concreting in freezing weather. 


PROPERTIES OF CONCRETE 


Compressive Strength.—In general, the compressive strength 
of concrete depends on the water-cement ratio in the mix, pro- 
vided the concrete is of a workable consistency. This strength 
may be appreciably lessened by poor materials (cement, water, 
and aggregates), presence of impurities, too little mixing, poor 
placing, and improper curing or hardening. The unit compres- 
sive strength at 28 days is given by the formula: 


14,000 
Ss = 7a 
where S = unit compressive strength at 28 days 
x = water-cement ratio by volume 


CONCRETE PRACTICE 


18 


Due to poor materials or poor working conditions, the above 
formula may give a greater strength than is actually obtained on 
the job. When there is some doubt as to the quality of the 
materials, the presence of impurities, or the correctness of the 


ATT 
SPRRTOTAADTRARRAEAREDOTODORU ADAGE ODATOIAEDE AAs 
HUET 
LTT TTT be 

HE eee Rca il es Us 
| 

/ 

L 


Pin ET ee 
TT TT 
TTT TTT 
Oe 
et TMC 
AANA 
Ss S 
$ S 


S Ss S S 
g 8 8 8 


Ul OS 420 Gf - SK Bp 5 82 10 YJOUBMS AA. 1ssasclulo > =S 


x= Water Cernent RaH0 


Water - gallons per bag of cement 
300 ae 450 $25 6.00 675 750 825 900 975 /050 
Fria. 3.—Relation between the compressive strength of concrete and the water 


50 60 70 80 .90 100 110 120 130 140 150 


0 


cement ratio. 


14,000 


proportioning, mixing, placing, or curing, the number 7 in the 
formula should be replaced by 9. This strength formula then 
becomes: 


FUNDAMENTAL CONSIDERATIONS 19 


The curves in Fig.°3 show the relation between the unit 28-day 
compressive strengths and the water-cement ratios by volume, 
plotted according to the above formulas. 

Other formulas, which will give practically the same results for 
water-cement ratios varying from 0.6 to 1.6 (unit compressive 
strengths varying from 4500 to 600 lb. per sq. in.), are: 


Ss = _™ = 1700 for good working conditions 


and 


2 ay) 
S = oe — 1700 for poor working conditions 


If desired, gallons of water per sack of cement may be used 
instead of the water-cement ratio. Then, letting g.s. equal the 
gallons of water per sack of cement, these formulas may be 
written: 


S = a — 1700 for good working conditions 


or 
27,700 
esis 1.700 


and 


S= 7 — 1700 for poor working conditions 


or 
24,400 
eS 431700 


For concrete mixes of equal workability, as measured by the 
slump test (see Appendix 7), there appears to be a relation 
between the amount of cement in the mix, the water-cement ratio 
necessary, the resultant compressive strength of the concrete, 
the maximum size of the aggregate, and the grading of the 
aggregate expressed in terms of the fineness modulus. This 
relation is shown graphically by the curves of Fig. 4. In general, 
the amount of cement and workability (slump) of the mix 
remaining the same, aggregates having greater fineness moduli 
and larger maximum sizes will require lesser amounts of mixing 


20 CONCRETE PRACTICE 


water per sack of cement (lesser water-cement ratios), and thus 
give concretes of greater compressive strengths. 


be Slump - 3 fo 4-in. Be 


8 AN b&b © 
Re eee es 
ae 
{ee 


Leaee 


0) 


fA 


i) 


Roe Oe ee 
Pa eS ee 


~ 


| Stump 6 40 Pin | | | | 
| 
BERR EL. 


N 


KR 


s Ce aoa fo Sa ae es ee ad ee ee 


Wy 


us) 


Real M/x.— Volumes of Mixed Aggregate for each Volurne of Cement 
S 


50 54 58 62 66 70 46 50 54 58 62 66 7.0 72 
Fineness Modulus of Aggregate 


Fig. 4.—Relation of size and grading of aggregate and quantity of cement to 
strength of concrete. This diagram is based on the relation between strength 
and quantity of mixing water shown by Curve B in Fig. 3. ; 


With good curing conditions, there seems to be a fairly definite 
relation between the unit 7-day and 28-day unit compressive 
strengths of the concrete. This relation is shown by the formula: 


Seg = S; + 30S; 


FUNDAMENTAL CONSIDERATIONS 21 


wm 

oy 

ee 

ATE 
aver 

% Pel / aha bel 
> 7A ae ee 
= QUE ah 
= Be neavicial 
Re ees | 
EN peal ae 
< PEEL 
a SaMRnee 
S “mbaes 
& Sunngee 
wv el. ia 
~ a a 
ze i 
Q 
: PEE 
: 
G 

@ 


—_ 


528 


/000 


Af | 
74 Sac aetee og 
aA eee 
Cee ee ee 
0 /000 2000 3000 4000 5000 
57= Compressive Strength at 7 days 


Fic. 5.—Compressive strength of concrete—seven and twenty-eight day 
strength relation. 


Revert fe 
me, 
| | 


ray 
Period of Curing, in years 
Fic. 6.—Strength-age curve for concrete. 


22 CONCRETE PRACTICE 


where 

Ses = unit 28-day compressive strength 
and 

S; = unit 7-day compressive strength 


The curve in Fig. 5 shows the relation between the 7- and 28-day 
unit compressive strengths. 

The unit compressive strength of concrete increases with age, 
about as shown by the curve in Fig. 6. Of course, variations in 
the qualities of the materials used and in the curing conditions 
will affect the compressive strength, and may give values which 
are more or less than those shown by the latter part of the curve. 

Weight per Cubic Foot.—The weight per cubic foot of good 
sand and crushed stone or gravel concrete varies from about 135 
to 160 lb. per cu. ft., with an average value of about 145 lb. per 
cu. ft. for plain concrete. Concrete made from cinders, slag, and 
other light aggregates will have a lighter unit weight than the 
values given. 

Expansion and Contraction.—Concrete will frequently shrink a 
little when hardening in air, and may keep the same volume or 
expand a little when hardening in water. The coefficient of 
expansion for concrete is about 0.000006 per °F., and this coeffi- 
cient varies but little for the different mixes and aggregates com- 
monly used. The fact that a good crushed stone or gravel 
concrete has about the same coefficient of expansion as steel 
means that temperature changes will not cause the separation of 
the concrete and steel in reinforced concrete work. 

Absorption.—The absorption of water by plain concrete may 
be comparatively small or great, depending on the density of 
the mix, richness of the mix, kind of aggregates used, and the 
thoroughness and care used in proportioning, mixing, placing, 
and curing. In general, the same factors that tend to make a 
concrete mix waterproof will also tend to make it non-absorptive. 

Abrasion.—The abrasive resistance of plain concrete depends 
primarily upon the abrasive resistance of the mortar, which in 
turn depends upon the ability of the cement to hold the sand 
grains together, and upon the abrasive resistance of the sand 
grains themselves. When the surface of the concrete is worn 
away, so that the coarse aggregate is exposed, the abrasive 


FUNDAMENTAL CONSIDERATIONS 23 


resistance then depends partly upon the abrasive resistance of 
the coarse aggregate. 


Exercises.—Using both curves of Fig. 3, find the unit ultimate 28-day 
compressive strengths for a mix having a water-cement ratio of 0.90. Fora 
water-cement ratio of 1.05. For a water-cement ratio of 1.20. 

If the unit ultimate compressive strength of the concrete was 1770 lb. per 
sq. in. at an age of 7 days, what would be its probable strength at an age of 
28 days? 

If the unit ultimate 28-day compressive strength of concrete was 2400 lb. 
per sq. in., what would be its probable unit strength at 6 months? (Sug- 
gestion: Use curve showing relation of strength to age.) 

How many inches wouid a concrete wall 80 ft. long expand, when the 
temperature increases from 45 to 90°F.? 


EFFECTS OF VARIOUS SUBSTANCES ON CONCRETE 


Tne effects of various substances on concrete may be divided 
into two classes: (1) the effect of various substances mixed with 
the concrete; and (2) the effect of various elements on the 
concrete. 

Effect of Mixing Various Substances in Concrete. Azr.—dAir 
is the most common impurity present, as evidenced by air voids 
in the concrete. Most of the air may be removed by thoroughly 
‘compacting the concrete in the forms. 

Clay and Silt.—A little finely divided clean clay or silt tends 
to make concrete (especially the leaner mixes) more water tight 
and more easy to work. An excess of clay or silt (say more than 
10 per cent) may cause a decided loss of strength. 

Loam and Dirt.—These materials, if organic matter is not 
present, have about the same effect as clay and silt. As organic 
matter is usually present in loam and dirt, these materials should 
be excluded from concrete mixes. 

Organic Matter.—All organic matter should be excluded from 
concrete mixes, because as small an amount as 149 of 1 per cent 
may be very injurious. 

Lime.—Unhydrated lime (quick lime) should never be added to 
a concrete mix, as its expansion when hydrating will probably 
cause expansion and disintegration of the concrete. ‘Thoroughly 
hydrated lime has about the same effect as clay, and is preferable 
to clay. 


24 CONCRETE PRACTICE 


Mica.—A very small amount of mica mixed in concrete will 
cause a decided loss of strength. 

Sugar.—The presence of a small percentage of sugar mixed 
with the concrete reduces the strength and soundness of the 
concrete. 

Grease and Oil.—These materials have a bad effect on the quali- 
ties of concrete, when mixed with the concrete materials. 

Sea Water.—It is not thought advisable to use sea water as 
mixing water, when making concrete, though recent tests have 
not shown a very great loss in strength. 

Salt Water.—Waters, containing more than a few per cent 
of common salt in solution, may cause a decided loss in strength, 
and, consequently, salt should not be added to the mixing water. 

Acid and Alkali Waters.—Mixing waters containing much acid 
or alkali frequently reduce the strength and soundness of the 
concrete. 

Effect of Various Elements on Hardened Concrete. /Fire.— 
Good concrete is little affected by fire up toa temperature of about 
1200°F. (as hot as an ordinary fire). The action of fire is to cause 
a change in a thin layer of the outer surface of the concrete, and 
this layer then serves to protect the remainder of the concrete. 
Aggregates, which will burn or disintegrate under temperatures 
less than 1700°F., should not be used in concrete which may be 
subjected to fire. A fire hot enough to cause disintegration of 
the aggregates will, of course, cause a failure of the concrete. In 
some cases, the expansion and contraction, due to the application 
of fire and streams of water, may cause trouble. In general, 
concrete has better fire-resisting qualities than ordinary building 
stone, brick, tile, or terra cotta. 

Frost.—In general, freezing has little effect on good, well- 
hardened concrete. Freezing and thawing of wet and com- 
paratively porous concrete frequently cause disintegration and 
spalling of the exposed surfaces. | 

Sea Water.—Sea water appears to have little effect.on good, 
dense, concrete, well made from materials of excellent qualities. 
Poor concrete, when exposed to sea water, often shows a swelling, 
cracking, and crumbling of the surfaces. 

Alkali.—The effect of alkali water is practically the same as 
that of sea water. 


FUNDAMENTAL CONSIDERATIONS 25 


Oils and Greases.—The effect of various oils and greases is 
given in Appendix 10. 

Acids.—In general, good, thoroughly hardened concrete is 
affected only by such acids as would seriously injure other 
materials. 

Miscellaneous Liquids.—The effect of various liquids often 
found in different manufacturing processes is given in Appendix 
10. 


Exercises.—What is the general effect of the following materials on the 
surface of good, thoroughly hardened concrete, and what surface treat- 
ment is recommended (see Appendix 10). Heavy oils? Gasoline? Olive 
oil? Cider vinegar? ‘Tanning liquors? 


SECTION II 


PROPORTIONING, MIXING, AND PLACING CONCRETE 


JOB 1. GENERAL THEORY OF CONCRETE PROPORTIONING 


Fairly recent investigations have shown that the strength of 
concrete depends primarily on the water-cement ratio (ratio of 
volume of water to volume of cement) of the mix, provided the 
mix is of a workable consistency. Increasing the amount of 
cement, or decreasing the amount of water, decreases the water- 
cement ratio and increases the strength, and vice versa (see Fig. 
3). The least amount of water that will give a workable mix will 
also give the strongest concrete. 

Both the economy and the workability of the mix are influenced 
by the grading and size of the aggregate. An increase in the 
fineness modulus (see page 9) and maximum size of the aggre- 
gate will usually be advantageous. For example, it has been 
found that, with a fixed amount of cement and water (constant 
water-cement ratio), the same quantity of a given aggregate will 
always be required to give a mix of a desired workability. The 
same workability may be obtained by using a greater quantity of 
an aggregate having a larger fineness modulus and larger maxi- 
mum size. Likewise, the same workability may be obtained by 
using a lesser quantity of an aggregate having a smaller fineness 
modulus and smaller maximum size. Hence, for a mix having a 
definite strength (water-cement ratio) and a certain workability, 
the most economical aggregate to use is one having the largest 
permissible fineness modulus and maximum size. By largest 
permissible maximum size is meant that the aggregate must not 
be so large as to restrict a free flow of the concretein the formsand 
around the reinforcement. By largest permissible fineness 
modulus is meant that the aggregate must not have an excess of 
large particles so as to make the mix harsh. The amount of the 

26 


PROPORTIONING, MIXING, AND PLACING CONCRETE 27 


fine aggregate in the mix should not be less than half of the 
amount of the coarse aggregate. 

The required consistency or workability of the mix will vary 
for different jobs. For example, a much drier mix can be used 
for massive concrete work, such as large retaining walls or bridge 
abutments, than for a thin wall or a reinforced concrete floor. 

The water-tightness of a concrete mix may be increased by the 
careful grading of the aggregates and the correct proportioning 
of the materials, so as to make the resultant mix more dense and 
to reduce the size and number of the voids. 

Only materials of good quality should be used for concrete 
mixes. ‘The portland cement should be one which has passed the 
standard specifications and tests. Water and aggregates of good 
quality should be selected as explained in Section I. 

From the above statements, the following general rules for 
proportioning concrete may be deduced: 

1. Use portland cement, water, and aggregates of good quality. 

2. Base the strength on the water-cement ratio. 

3. Base the required workability of the mix on the particular 
job, using as dry a mix as practicable. 

4, Add mixed aggregate to the cement and water, to give the 
desired workability of mix. 

5. For economy, grade and combine the fine and coarse aggre- 
gates, so that the greatest proportion of mixed aggregate can be 
used and yet have a mix of the desired workability. 

For years, different investigators have tried to find a general 
rule for proportioning concrete by which its qualities and prop- 
erties could be determined in advance. While no such general 
rule has been found and accepted by all concrete engineers, much 
worth-while knowledge has been obtained in regard to the 
proportioning of concrete mixes. This knowledge, intelligently 
applied, greatly reduces the amount of work required to produce 
a concrete mix having the desired qualities. 

The effects on the qualities of the concrete mix, due to varying 
the water-cement ratio and the amounts and grading of the 
aggregates, have been fairly well determined. The effects caused 
by using aggregates of different types and kinds need to be more 
fully investigated. To quote the Bureau of Standards: ‘‘No 
type of aggregate such as granite, gravel, or limestone can be said 


28 CONCRETE PRACTICE 


to be generally superior to all other types. There are good and 
poor aggregates of each type.” 

Consequently, the best and safest way of determining the cor- 
rect proportions for a concrete mix using any one kind of aggre- 
gate is, first, to test the materials to be used, then carefully select 
the proportions according to the best information available, and 
lastly to check the qualities of the mix selected by strength and 
other tests. 

The methods of proportioning concrete given in the following 
articles have been used at various times and places. Propor- 
tioning with reference to the water-cement ratio, consistency, 
and fineness modulus of the aggregate is the method recom- 
mended. 


JOB 2. PROPORTIONING CONCRETE BY ARBITRARY 
PROPORTIONS 


This method is the oldest and most commonly used method in 
this country. The materials are measured by volume, with 1 
cu. ft. as the common unit of measurement. One sack of cement 
is taken as 1 cu. ft., and the fine and coarse aggregates are usually 
measured by volume in a loose condition, just as they are thrown 
into a wheelbarrow or measuring hopper. Enough mixing water 
is used to give the mix the desired consistency, which is frequently 
much wetter than necessary for the best results. Proportioning 
concrete by volume, by the method of arbitrary proportions, is 
proportioning by a rule-of-thumb method which is not justified 
either by science or good practice. 

The following are some of the commonly used mixes: 

1:1:2 A very rich mixture used where great strength and 
water-tightness are required. 

1:1:3 A rich mixture not so strong as the preceding, but used 
for the same purposes. 

1:2:4 A good mixture, used very often for reinforced concrete. 
Often assumed to have a compressive strength of 2000 
lb. per sq. in. at an age of 28 days. 

1:2:5 A medium mixture used for plain concrete floors, retain- 
ing walls, abutments, etc. 

1:3:6 A lean mixture used for massive concrete under steady 
loads of not great intensity. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 29 


1:4:8 A very lean mixture used only for massive concrete, which 
supports practically no load except its own weight. 

Sometimes the proportions of the mix are given as one part 
by volume of portland cement, to a number of parts by volume 
of combined fine and coarse aggregates. Some of these mixes 
frequently used are as follows: 

1:5 About the equivalent of the 1:2:4 mix previously given. 

1:6 About the equivalent of the 1:2:5 mix previously given. 
This 1:6 mix is often substituted for a 1:2:4 mix, but con- 
tains less cement per unit volume of concrete and has less 
strength than the 1:2:4 mix. 

1:9 A very lean mix, equivalent to the 1:4:8 mix previously 
given. This 1:9 mix is often substituted for a 1:3:6 mix. 

A 1:2:4 mix by volume is about the equivalent of a 1:5 mix 
by volume, because most of the fine aggregate in the 1:2:4 mix 
goes to fill the voids in the coarse aggregate, and the resulting 
volume of the mixed aggregate is not 6, but about 4.75. The 
weight per cubic foot of a combined aggregate is invariably more 
than that of either the fine or the coarse aggregates taken 
separately. 

If the proportions were given by weight, then a 1:2:4 mix 
would be the equivalent of a 1:6 mix, because 1 lb. of cement. 
plus 2 lb. of sand plus 4 lb. of stone is about the same as 1 lb. of 
cement plus 6 lb. of mixed sand and stone (exactly the same if 2 
Ib. of sand are mixed with 4 lb. of stone to give the combined 
aggregate). 


Exercises.—What “standard” mix by volume is commonly used for 
reinforced concrete work? | 

What mix by volume is commonly used for basement walls? 

Show that a 1 : 9 mix by volume of cement to combined aggregate is not 
the same as a 1:3:6 mix by volume of cement to fine aggregate to coarse 
aggregate. If a numerical problem is desired, assume the weights of 
cement, and fine and coarse aggregates to be 100 Ib. per cu. ft., and the 
weight of the combined aggregate to be 125 lb. per cu. ft. 


JOB 3. PROPORTIONING CONCRETE WITH REFERENCE TO VOIDS 


The object of this method of proportioning is to secure a con- 
crete mix having a minimum percentage of voids, the idea being 
that, with other things equal, the densest mix (mix with the least 


30 CONCRETE PRACTICE 


voids) will make the strongest and best concrete. It is doubtful 
if this method of proportioning is of much practical value unless 
checked by strength and other tests. 

There are several variations of this method of proportioning of 
which the following three methods are the most common: | 

One variation is to use just enough mortar to fill the voids in 
the coarse aggregate. Due to the bulking effect, however, about 
10 per cent more mortar is required. Coarse aggregates having a 
low percentage of voids permit a saving of cement and sand. 
The strength of the mix is to be increased or decreased by varying 
the amount of cement in the mortar. 

Another variation is to mix the fine and coarse aggregates in 
such proportions that the resulting voids will be a minimum, and 


then to add the cement and water. The strength of the mix is. 


to be governed by the amount of cement added. 

A third variation (and possibly the best one) is to try several 
trial mixes of cement, water, and fine and coarse aggregates to 
find a mix that will be the most dense (have the least voids). It 
is assumed that this mix will be the strongest and most impervious. 


JOB 4. PROPORTIONING CONCRETE BY SIEVE ANALYSES OF THE 
AGGREGATES AND THE MAXIMUM DENSITY CURVE 


In this method of concrete proportioning, it is assumed that 
the densest mix can be secured by making sieve analyses of the 
aggregates (both fine and coarse); and then combining these 
aggregates and the cement with the aid of the maximum density 
curve. ‘This method may be considered a variation of the void 
method, in which the proportions of the densest mix are secured 
by the help of the sieve analyses and the maximum density curve. 

After the sieve analyses of the aggregates have been made, the 
results are plotted on cross-section paper, and a curve drawn 
for each aggregate. Percentages passing sieves are plotted to a 
vertical scale (ordinates), and diameters of sieve openings are 
plotted to a horizontal scale (abscissae). 

Then a maximum density or ‘‘ideal’”’ curve is drawn. ‘This 
curve consists of a straight line and a portion of an elliptic curve. 
The straight line is drawn from the intersection of the maximum 
size of coarse aggregate line, with the 100 per cent line tangent to 
the elliptical curve. The abscissae of this point of tangency is 


PROPORTIONING, MIXING, AND PLACING CONCRETE 31 


equal to one-tenth of the maximum size of the coarse aggregate, 
and the ordinate (or height of the tangent point) is equal to 35.7 
per cent for crushed stone and sand, 33.4 per cent for gravel and 
sand, and 36.1 per cent for crushed stone and screenings. 

When a fixed proportion of cement in respect to the total aggre- 
gate is used, various combinations of the fine and coarse aggre- 


100 = E 9 
Paeamme mh... 
Sa a A 
Pee ee ay | 
oo) Te a ees 
ee eee | eee et 
wl) Se sae aa 
ee oe ee: 
eee eee | ey tt 
caine aeenmere cae iE ey Ee ee 
pel oe 
J 2 Ane eee: 
tts ttt ete t+ tot ¢ 
ll ASS a2) eee eee: 
i el 2 a a2 
oh 
oS TES a 
ee eo a ee 
de ee PSSA PRS es Es a eae 


ioe 
meeeeea io te ee 
eee er 


ie) 010 H 920 030 050 060 0.70 080 0.90 1.00 
Bye cece of Particle in Inches. 


Fic. 7.—Maximum density and combined aggregate curves. 


gates are tried, and the curves of the trial mixes are plotted until 
a mix is found, whose curve agrees fairly well with the maximum 
density or “‘ideal” curve. Sometimes itis necessary to screen the 
coarse aggregate into two or more sizes, in order to obtain the 
densest and best mixture. 

For a good working concrete, the portion of the trial curve over 
_ the smaller sieve diameters should not fall below the ‘ideal’ 
curve, as it is better to have a slight excess of fine material in the 
mix. In regard to the portion of the trial curve over the larger 


32 CONCRETE PRACTICE 


sieve openings, it is immaterial whether the trial curve is a little 
above or a little below the ‘‘ideal”’ curve. 

This method of proportioning is not thought to be of great 
practical value in designing concrete mixes for strength, because 
it has been found, in many instances, that trial mixes, whose 
curves did not closely approach the ‘‘ideal”’ curve, often were as 
strong as the trial mix whose curve agreed the closest with the 
‘deal’? curve. For years, however, this method appeared to 
have been the best method found, and, when checked by strength 
tests, usually gave good results. 

For designing impervious mixes, this method of obtaining the 
best proportions is very good, because the densest mix is nearly 
always the most water-tight mix. 


JOB 5. PROPORTIONING CONCRETE BY THE SURFACE AREA 
METHOD 


This method for finding the proportions for a concrete mix is 
based on the assumptions that the strength of concrete depends 
upon the amount of cement used in relation to the surface area of 
the aggregate, and upon the consistency of the mix. 

The general method of procedure for proportioning concrete 
by this method is as follows: 

1. Make sieve analyses of the aggregates. 

2. Find the average number of particles per unit weight of the 
ageregate passing one sieve and held on another. 

3. From the results of (2), and the specific gravity of the 
particles, compute the average volume of each size of particle. 

4. Compute the surface areas from the average volumes of the 
various sizes and shapes of the particles. (Grains of sand and 
gravel are assumed as spherical, while particles of broken stone 
are assumed to be one-third cubes and two-thirds parallelopipeds. ) 

5. Determine the total surface area of the aggregates. 

6. Base the quantity of cement on the total surface area. 

7. Base the quantity of water on the quantity of cement and 
the total surface area of the aggregates. 

8. Make strength tests on the mortar or concrete as deter- 
mined in (7). 

9. Increase or decrease the cement and water content of the 
mix until a mix is found that gives the required strength. The 


PROPORTIONING, MIXING, AND PLACING CONCRETE 33 


correct water-cement ratio must always be maintained, or else 
the results will not be satisfactory. 

The work required for this method of proportioning can be 
simplified in the laboratory by the use of curves and tables, 
showing the relations between surface areas and unit weights 
of particles of various shapes and sizes and specific gravities, 
water-cement ratios, and the relations between strength and 
cement content and surface areas, ete. 

Results of tests do not appear to prove the correctness of the 
assumptions made for this method of proportioning, but tend to 
show that the surface area and consistency of mix are only two of 
several factors affecting the properties of the concrete. 


JOB 6. PROPORTIONING CONCRETE BY THE USE OF THE TABLES 
IN THE 1924 REPORT OF THE JOINT COMMITTEE 


If instructions are carefully followed, the tables given in 
Appendix 6 (taken from the 1924 Report of the Joint Committee) 
may be used to obtain the proportions of a concrete mix which 
will have a required compressive strength at an age of 28 days. 
These tables naturally cannot take into consideration all of the 
different types and kinds of aggregates and, consequently, there 
may be some aggregates for which the tabulated proportions will 
not give the desired strength results. Therefore, whenever time 
permits, control tests should be made to check the proportions 
selected from the tables. 

When using these tables, it is assumed that good portland 
cement, clean mixing water, and clean and structurally sound 
aggregates are to be used in the concrete. The tables include 
possible variations in the size and grading of the aggregates, and 
in the consistency of the mix, as shown by the slump test. 

The tables in Appendix 6 are to be used: 

1. To furnish a guide in the selection of mixtures to be used in 
preliminary investigations of the strength of concrete from given 
materials. 

2. To indicate proportions which may be expected to produce 
concrete of a given strength under average conditions where 
control tests are not made. 

The method of procedure in selecting proportions from these 
tables is as follows: 


34 CONCRETE PRACTICE 


1. Decide on the unit compressive strength to be required of 
the mix. (This is usually stated by the designing engineer or 
architect. ) 

2. Select the consistency of mix to be used on this particular 
job. (This is usually stated by the designing engineer or 
architect. ) 

3. Obtain representative samples of the fine and coarse aggre- 
gates, and determine their maximum and minimum sizes by mak- 
ing sieve analyses, using the sieves given in the tables. Apply 
the rules given on the first page of Appendix 6 when determining 
the size of a given aggregate to be used in connection with the 
tables. 

4, Select the required mix from the tables, interpolating for 
strengths, aggregate sizes, and consistencies when necessary. 

The proportions listed in the tables are by volumes of cement 
(based on 94 lb. equaling 1 cu. ft.) to volumes of fine and coarse 
ageregates compacted by rodding in the measuring box, as 
specified in the Standard Method of Test for Unit Weight of 
Aggregate for Concrete (Appendix 2). 

In laboratory work, it is advisable to find the weights per cubic 
foot of the aggregates (as directed in Appendix 2) and then 
change the proportions by volume to proportions by weight. 


Exercises.—Given a sand which passes a No. 4 sieve and has 16 per cent 
retained on a No. 8 sieve, and a crushed stone which passes a 1 %-in. sieve, 
has 18 per cent retained on a 1-in. sieve, has 19 per cent passing a 3¢-in. 
sieve, and has 4 per cent passing a No. 4 sieve. 

a. Select proportions for a mix to give a 28-day compressive strength 
of 2500 lb. per sq. in. with a consistency of mix to have a slump of 6 in. 

b. Select proportions for a mix to give a 28-day compressive strength 
of 2750 lb. per sq. in. with a consistency of mix to have a slump of 8 in. 

If the unit weights of the cement, sand, and crushed stone in the preceding 
question are 94, 110, and 100 lb. per cu. ft., respectively, compute the 
proportions by weight for the mixes selected for parts (a) and (0). 

Given a sand having 3 per cent retained on a 3-in. sieve and 22 per cent 
retained on a No. 4 sieve, and a gravel having 2 per cent retained on a 1 }-in. 
sieve, 30 per cent passing a 34-in. sieve, and 12 per cent passing a 3¢-in. 
sieve. 

a. Select proportions for a mix to give a 28-day compressive strength of 
2000 Ib. per sq. in. with a slump of 8 in. 

b. Select proportions for a mix to give a 28-day compressive sthenieth of 
3000 lb. per sq. in. with a slump of 4 in. 


eS a 


PROPORTIONING, MIXING, AND PLACING CONCRETE 35 


JOB 7. PROPORTIONING CONCRETE BY THE WATER-CEMENT 
RATIO AND SLUMP TEST 


In proportioning concrete by this method, the water-cement 
ratio is used to determine the compressive strength of the con- 
crete, and the slump test to determine the workability or con- 
sistency. There are three rules to be observed: 

1. Use the exact amount of water with each sack of cement to 
produce the desired compressive strength. If there is water 
present in the aggregates, this water must be included when 
determining the amount of water used for the mix. 

2. Use enough mixed aggregate with the cement and water to 
give a concrete mix of the consistency needed for the particular 
work in question. This consistency should be specified by the 
slump in inches. | 

3. If the amount of work warrants, mix the fine and coarse 
aggregates so that as large a proportion of mixed aggregate as is 
practical may be used with the cement and water, and yet have a 
mix of the desired consistency. In general, to avoid the possi- 
bility of a harsh mix, the weight of fine aggregate in the combined 
or mixed aggregate should not be more than the weight of the 
coarse aggregate, or less than half the weight of the coarse aggre- 
gate. In the mixed aggregate, the fine aggregate shall be that 
passing (finer than) a No. 4 sieve, and the coarse aggregate that 
retained on (coarser than) a No. 4 sieve. 

For work in the field or laboratory, where the proportioning of 
the mix is accurately controlled, the gallons of water required per 
sack of cement for a desired 28-day unit compressive strength 
may be found from Curve A (Fig. 3), on page 18, or by the 
formula: 


27,700 
Gallons of water per sack of cement = S + 1700 


where S is the 28-day unit compressive strength. Sometimes 
the gallons of water per sack of cement found by Curve A or the 
above formula are reduced by 14 gal. per sack of cement to allow 
for slight errors in measuring the water. 

For practical work, where it is more difficult accurately to 
control the proportioning of the mix, the values recommended for 


36 CONCRETE PRACTICE 


use are those given by Curve B, (Fig. 3), page 18, or by the 


formula: 
24,400 


S + 1700 

These proportions of water to cement have been based on the 
results of a great many tests, and, consequently, may be expected 
to give the desired results in nearly every case. The tests, 
however, have not taken into consideration every kind and type 
of aggregate which may be used in concrete, and there may be 
some aggregates for which the values given in the tables will not 
apply. When there is any doubt, control tests should be made 
as a check on the compressive strength and other qualities of the 
mix. 

For field work, 1 U.S. gal. of water may be considered as 231 
cu. in., or 8.35 lb. One cu. ft. of water weighs 62.35 lb., and 
contains about 7.5 (7.48) U.S. gallons. 

The amount of water or moisture contained in the aggregates 
must be found and considered when determining the number of 
gallons of water required per sack of cement. The aggregates 
should be stored and handled on the job, so that the moisture 
content of the aggregates will not be subject to frequent or 
unnecessary changes as they come to the mixer. ‘The amount 
of moisture in an aggregate is rarely less than 2 per cent by 
weight, is usually between 3 and 4 per cent, and often is as 
much as 6 or 8 per cent directly after a rain. The absorption 
of various aggregates, expressed as a percentage of their dry 
weight, will average 1.0 per cent for average sand, 1.0 per cent 
for gravel and crushed limestone, 0.5 per cent for trap rock and 
granite, from 5 to 10 per cent for porous sandstone, and up 
to 25 per cent for very light and porous aggregate. 

The amount of moisture contained in an aggregate may be 
found by first weighing and drying a 10- or 20-lb. sample to a 
constant weight, and then weighing again. The difference 
between the two weights gives the amount of moisture contained 
in the sample. The percentage of moisture should preferably be 
expressed in terms of the dry weight of the aggregate. 

The consistency of the mix should be determined by the slump 
test (Appendix 7). The following maximum values of the slump 
in inches should not be exceeded: 


Gallons of water per sack of cement = 


PROPORTIONING, MIXING, AND PLACING CONCRETE 37 
sa a a a 


Maximum 
Kind of concrete slump, 
inches 
Ste ie cc rr 
Plain concrete: 

Mass concrete (foundations, basement walls, thick floors, 


eM ee) oe ak ee ea Sh Oe ee been. 3 
Comparatively thin sections (basement floors)............ 6 
Hand-finished roads and pavements..................... 3 
Machine-finished roads and pavements....... - 1 
teen eee? STII ast yes ce be ds ve ca cabs eusce. 2 

Reinforced concrete: 
Columns and thin, vertical sections (thin walls and parti- 

Gata ike Sie gc Sie cgcecea ee cawa’ 6 
Heavy vertical and horizontal sections (thick walls, thick 

eM OE Se aa wie wie Sed wns Ghled eb oodh ame os 3 
Thin, confined, horizontal sections.....................5. 8 
Muusoors and shallow beams...........0 6.06.0. eee ee 6 


For an illustration of this method of proportioning, suppose 
that it is desired to find the proportions of cement, water, and 
mixed aggregate for a concrete mix to have a 28-day compressive 
strength of 2000 lb. per sq. in., and a slump of 6 in. 


From Curve A (Fig. 3) page 18, it is seen that 7.5 gal. of water per sack 
of cement are needed. Deducting 0.25 gal. per sack of cement for possible 
errors in mixing, the amount of water to be used on the job will be 7.50 — 
0.25 or 7.25 gal. per sack of cement. 

Assume that a suitable mixed aggregate (maximum size 114 in.), as mixed 
on the job, contains 2 parts of fine aggregate to 3 parts of coarse aggregate 
by volume, and weighs 115 lb. per cu. ft. 

Also assume that under average working conditions, the average moisture 
content of the mixed aggregate is 3.0 per cent, and the absorption is 1.0 
per cent. Then the net moisture available for use in the mix is 3.0 — 1.0 or 
2 per cent of the dry weight of the aggregate. The dry weight of the mixed 
aggregate. will be 115 — 115 X 0.03 = 111.5 lb. per cu. ft. 

A 1:4 mix will be tried. The amount of water in the mixed aggregate will 
be 4 X 111.5 X 0.02 = 8.92 lb., or 1.1 gal. 

Suppose that the 1:4 mix by volume with 7.25 — 1.1 or 6.15 gal. of water 
per sack of cement is tested for slump, and that the slump is found to be 7 in., 
indicating that more aggregate can be used. 

Assume, then, a 1:4.5 mix. The amount of water to be added will be 


' 4.5 X 111.5 X 0.02 
025 — ( 3.35 


Suppose that this mix gives aslump of 6}4 in. and is satisfactory. 


= 6.05 gal. of water per sack of cement. 


38 CONCRETE PRACTICE 


The field proportions of the mix will be: 1 sack of cement to 6 gal. of 
water to 4.5 cu. ft. of mixed aggregates, mixed in the proportions of 2 parts 
of fine aggregate to 3 parts of coarse aggregate by volume. ‘This field mix 
may be reasonably expected to give a concrete with a 28-day unit compres- 
sive strength of 2000 lb. per sq. in., and at the same time permit an excess 
of 0.25 gal. of water per sack of cement in any one batch. 

Exercises.—State the three rules or principles governing the proportioning 
of concrete by the above method. 


JOB 8. PROPORTIONING CONCRETE BY THE WATER-CEMENT 
RATIO, SLUMP, AND FINENESS MODULUS OF AGGREGATE 
This method of concrete proportioning is based on fairly 

definite relations between the strength and water-cement ratio, 
and between the consistency (workability of the mix as measured 
by the slump test) and the grading of the aggregates as denoted 
by the fineness modulus. The compressive strength is deter- 
mined by the water-cement ratio, the workability or consistency 
by the slump, and the economy by the grading of the aggregate 
as evidenced by the sieve analysis and fineness modulus. 

The fineness modulus, a term used to denote the effective grad- 
- Ing of the aggregate, is equal to one-one hundredth of the sum of 
the percentages of the aggregate retained on (coarser than) the 
following square mesh sieves: Nos. 100, 50, 30, 16, 8, 4, and 3 in., 
34 in., and 114 in. Each sieve has a clear opening just double 
that of the preceding sieve. The sieve openings and the method 
of making the sieve analysis should conform to the specifications 
of Appendix 38. The coarser the aggregate, the higher the fineness 
modulus. 

Tests have shown that mixtures of fine and coarse aggregates, 
having the same fineness modulus and the same amounts of 
cement and water, produced concretes of equal workability or 
consistency and of equal strength, provided the concrete mix was 
plastic, and that the aggregates were not too coarse for the amount 
of cement used. The tests also showed that, for any given mix of 
cement and aggregate, as the coarseness of the aggregate (fineness 
modulus) increased, the amount of water required for a given 
workability decreased. In other words, larger quantities of 
coarser aggregates may be mixed with a given amount of cement 
and water, and yet have a mix of the same workability or slump. 

There is a limit, however, to the maximum fineness modulus 
(or coarseness of aggregate) which may be used for any given mix, 


PROPORTIONING, MIXING, AND PLACING CONCRETE 39 


as an aggregate which contains too many coarser particles will 
cause the mix to be harsh and to deviate from the strength rela- 
tion given by the water-cement ratio. The following table gives 
the approximate maximum permissible values of fineness modulus 
for aggregates of varying sizes and for different mixes: 


Maximum Practica VALUES OF FINENESS Mopu.us 


Volumetric ratio of cement to aggregate = real mix 


poet 1:1 ja | 1:3 | 1:4 | 1:5 | 1:6 | 1:7 | 1:9 
aggregate 
Maximum values of fineness modulus 
Mortars: 
Oy 16 Sena ee TOL 200.0) 42.00+) 2515. 12.05.) .1.95° 1.85 
aT ces as Seu oes o 3 10.) 2.90 | 2.75 12.66 | 2,55) 2.45 
(ne Be 4.75 | 4.20 | 8.90 | 3.60 | 3.45 | 3.30 | 3.20 | 3.05 
Concretes: 
O-— 3...... Deer Oo ) 4-70 | 4.404) 4.201) 4205-|.3:95 | 3.385 
PO owas ihGO,0n (5245 |:5,10 | 4:80 |) 4.60 | 4.45 |-4:35 | 4.25 
eo 7 GepOneo.o0) 5.50 (95:20, ).5.00 1.4.85 |} 4:75°) 4.65 
oe tS eet eee eee Seu ou | 0:90) 5.60 | 5.40 | 5.25 115.15 |. 5.00 
O-1\%....... peooe asi) | 6.30 1 6.00 1 5.80 | 5/65.) 6:55 | 5.40 
oy AE eee aoe 0 16-70 | 6340) 6220 1 6.05 |-5.95 |.5.:80 
Os Smee, Sevusereoo | {elo 6.85 |-6760 + 6.50 | 6.40 | 6.25 


ly, Half sieves not used in computing fineness modulus. 

For mizes other than those given in the table, use the values for the next leaner mix. 

For maximum sizes of aggregate other than those given in the table, use the values for the next 
smaller size, 


This table is based on the requirements of sand and gravel 
aggregate in ordinary uses of concrete in reinforced concrete 
structures. The values given in the table should be reduced by 
0.25 for crushed stone, slag, or screenings, and also for concrete 
work of comparatively thin sections. 

For concrete work, the practical limits of the fineness modulus 
for fine aggregates are from 2 to 4; for coarse aggregates, from 
5.50 to 8; and for mixed aggregates, from 4 to 7, depending upon 
the maximum size of the aggregate in question and the propor- 
tions and consistency of the mix. Fig. 4, on page 20, shows the 
relation in graphical form. 


40 CONCRETE PRACTICE 


The size of an aggregate may be determined by the following 
rules: 

1. Use ihe sieves listed in Appendix 3. 

2. Not less than 15 per cent of an aggregate shall be retained 
on the sieve next smaller than that considered as the maximum 
size. The minimum size of a fine aggregate is usually considered 
as 0. 

3. Not more than 15 per cent of a coarse aggregate shall be 
finer than the sieve considered as the minimum size (but more 
than 15 per cent shall be finer than the sieve which is next larger 
than that considered as the minimum size). 

The proportions of a real mix are by volume of cement (1 sack 
of 94 lb. assumed as 1 cu. ft.) to volume of dry, rodded, mixed 
aggregate. The proportions of a field mix are by volume of 
cement to volumes of aggregates as found and measured in the 
field. Consequently, the proportions of the two mixes may differ 
considerably. 

When the fineness moduli for the fine and coarse aggregates are 
known, the proportions in which to combine these aggregates to 
give a mixed aggregate having a desired fineness modulus (less 
than that of the coarse aggregate) may be found by the formula: 
Me —™M 
‘=e 

Me — Mf 
where 

m, m-, and my are the fineness moduli of the mixed, coarse, 
and fine aggregates, respectively. 7; is the ratio of volume 
of fine aggregate to the sum of the volumes of fine and coarse 
aggregates measured separately. 

: 3 

In a 1:3:5 mix, i, = 3 ak 0.375. 

This formula may be used to find the fineness modulus of the 
mixed aggregate when the proportions and fineness moduli of 
the fine and coarse aggregates are known. For convenience, the 
formula should be expressed in the following form: 3 


m = rsmMms +- ¢ oe rs)Me 


Note that (1 — ry) is the ratio of the volume of the coarse 
aggregate to the sum of the volumes of the fine and coarse 
aggregates measured separately. 


; 
| 


PROPORTIONING, MIXING, AND PLACING CONCRETE 41 


When fine and coarse aggregates are mixed together in certain 
definite volumetric proportions, the volume of the mixed aggre- 
gate will be less than the sum of the volumes of the fine and the 
coarse aggregates measured separately, because a large part of the 
fine aggregate will tend to fill the spaces or voids in the coarse 
aggregate. The ratio of the volume of the mixed aggregate to 
the sum of the volumes of the fine and the coarse aggregates is 
given by the following formula: 


rywr + (1 — ry). 
"a _ 
m 


where wy, W., and wm are the unit weights of the dry fine, coarse, 
and mixed aggregates, respectively. 

?m 18 the ratio of the volume of dry mixed aggregate to the sum 
of the volumes of the dry fine and dry coarse aggregates measured 
separately. | 

r; 1s the same as before. 

This ratio, 7m, 1s sometimes called the shrinkage factor, and is 
used in computing the proportions of the fine and the coarse 
aggregates in the real mix. 

The following method of procedure is suggested for finding the 
correct proportions, by this method, for a concrete mix to have a 
given compressive strength and slump. 

1. Secure representative samples of the aggregates and make 
any preliminary tests necessary to determine their cleanliness 
and quality, such as tests for silt and organic impurities. 

2. Determine the moisture content of the aggregates. 

3. Make sieve analyses of the aggregates and determine their 
fineness moduli and limiting sizes. 

4. Knowing the required strength and slump, determine the 
real mix and the fineness modulus of the mixed aggregate for this 
mix from the curves of Fig. 4, page 20. 

5. Compute the ratios of volumes of fine and coarse aggregates 
to give the required fineness modulus of the mixed aggregate in 
the real mix. 

6. Find the unit weights of the fine and coarse aggregates as 
they will be used in the field. 

7. Find the unit weights of the dry fine and the coarse aggre- 
gates according to the method of Appendix 2. 


42 CONCRETE PRACTICE 


8. Mix the dry fine and dry coarse aggregates in the propor- 
tions found-in Rule 5 above, and find the unit weight of the dry 
mixed aggregate according to the method of Appendix 2. 

9. Compute the ratio of the volume of dry mixed aggregate to 
the sum of the separate volumes of the dry fine and dry coarse 
aggregates. 

10. Compute the volumetric proportions of the cement, dry fine 
aggregate, and the dry coarse aggregate in the real mix. 

11. Determine the volumetric proportions of the field mix. 

12. Determine the amount of water required per sack of cement 
from the proper curve of Fig. 3, page 18, and compute the net 
amount of water per sack of cement to be added to the field 
mix. 

13. Mix a small batch of concrete in the required proportions 
for the field mix and determine the slump. If the slump found 
does not agree with that assumed, the mix must be repropor- 
tioned. To increase the slump a little, decrease the proportions 
of the aggregates slightly (say from 3 to 5 per cent), and vice 
versa. 

14. Observe if the batch made for the slump test is too harsh 
or not for the work in question. If the concrete is too harsh, the 
mix must be reproportioned using a lesser fineness modulus for 
the mixed aggregate. 

15. If time permits, make and test some cylinders made from 
a field mix as a check on the strength. 

Note that in the above procedure the strength of the concrete, 
and the gallons of water required per sack of cement, are based on 
Curve B of Fig. 3, page 18. If conditions in the field are such 
that Curve A of Fig. 3 may be used, the same procedure of deter- 
mining the proportions of the mix applies, if the following pre- 
liminary rule is observed: 

“Find the corresponding strength on Curve B for the same 
water-cement ratio, and then design the mix for this strength 
using the curves of Fig. 4.” : 

For example, the required proportions of a mix, to give a 
compressive strength of 2500 lb. per sq. in. under Curve A condi- 
tions, would be the same as the proportions needed to give a 
strength of 2000 lb. per sq. in. under Curve B conditions, 


PROPORTIONING, MIXING, AND PLACING CONCRETE 483 


Ezxercises.—If the size of the mixed sand and crushed stone aggregate in a 
concrete mix is 0:1} in., about what would be the maximum permissible 
value of the fineness modulus for a 1:4.4 real mix? 

What is the ratio of the volume of fine aggregate to the sum of the volumes 
of the fine and coarse aggregates measured separately, when the fineness 
moduli of the mixed, fine, and coarse aggregates are 5.20, 3.10, and 6.45, 
respectively? 

What would be the fineness modulus of a mixed aggregate containing 
40 per cent of fine aggregate, if the fineness moduli of the fine and coarse 
aggregates are 2.95 and 6.70, respectively? 

If a mixed aggregate contains 43 per cent of fine aggregate and the unit dry 

weights of the fine, coarse, and mixed aggregates are 107, 98, and 121 lb. per 
cu. ft., respectively, what would be the shrinkage factor or ratio of the vol- 
ume of the dry mixed aggregate to the sum of the volumes of the dry fine 
and dry coarse aggregates measured separately? 
__ If field conditions were such that the compressive strength of the concrete 
could be based on Curve A of Fig. 3, page 18, and the mix was to be designed 
for a compressive strength of 3000 lb. per sq. in., what strength value should 
be selected if the curves of Fig. 4 are to be used when designing the mix? 


JOB 9. ILLUSTRATIVE EXAMPLE OF PROPORTIONING CONCRETE 
BY THE WATER-CEMENT RATIO, SLUMP, AND FINENESS 
MODULUS OF THE AGGREGATE 


It was desired to proportion a concrete field mix to have a 
slump of about 7 in., and to give a 28-day compressive strength 
of 2000 lb. per sq. in. The job was comparatively large and field 
conditions were such that the proportioning of the aggregates 
could be (and were) accurately controlled, so that the use of 
Curve A of Fig. 3, page 18, was justified for determining the 
relation between the strength and water-cement ratio. 

~The method of procedure given in Job 8 was followed. 

Corresponding strength of mix from Curve B of Fig. 3 was 
- found to be 1550 lb. per sq. in. 

1. Representative samples of the fine and coarse aggregates 
were secured, and the aggregates tested and found satisfactory 
in regard to silt and organic matter. 

2. The moisture was determined and found to be 3.5 per cent 
for the sand, and 2 per cent for the crushed limestone by weight. 
The percentage of absorption was assumed as 1 per cent for both 
sand and crushed limestone. 

3. Sieve analyses of the dry aggregates were made, and the 
following results obtained; 


44 CONCRETE PRACTICE 


RESULTS OF SIEVE ANALYSES 


Sieves 


Aggregate 100 | 50 | 30 | 16 | 8 | 4 


34 | 134 


Percentages coarser than each sieve 


SAT) eet Gs te eat oe te oy 97.\ ‘78 |. 57). 380i eisteeo 0 0 0 
SEONG Ate Soy Tae oe is 100 | 100 | 100 | 100 | 100 | 97 | 68 | 82 3 
Fineness modulus of sand = 2.80, size Oto 4. 3 


Fineness modulus of stone = 7, size 4 to 14. 


4. From the curves of Fig. 4, page 20, a slump of 7 in., a Curve 
B strength of 1550 lb. per sq. in., and a maximum size of aggregate 
of 14% in., gave a real mix of 1:5.5 with a fineness modulus of 
5.65. 

5. Ratio of volume of fine aggregate to sum of volumes of fine 
and coarse aggregates measured separately was found to be: 

Me = «1 oD, 00 gee 
tT ney 1 2 80 
Similar ratio for coarse aggregate = 1—0.32 = 0.68. 

6. The unit weights of the aggregates as measured in the field 

were found to be: 


= 0.32 


Sand, damp and loose = 91.5 Ib, per eueae 
91.5 lb. damp, loose sand = 88.3 lb. when dry 
Stone damp and loose = 98 lb. per cu. ft. 


98 lb. damp, loose stone = 96 lb. when dry 
7. The unit weight of the dry, rodded aggregates were: 


Sand = 109 lb. per cu. ft. 
Stone = 103 lb. per cu. ft. 


8. The unit weight of the dry rodded mixed aggregate, in the 
proportion of 32 per cent sand and 68 per cent stone, was 121 lb. 
per cu. ft. 

9. Ratio of volume of dry, mixed aggregate to sum of separate 
volumes of dry fine and dry coarse aggregates was: 

pp ES + (1 ry) we 0.32 X% 108 0 be ae 
ae Wm ve 121 
foes) md OU ee O aro 


Searcy pom mr ik (shrinkage factor) 


PROPORTIONING, MIXING, AND PLACING CONCRETE 45 


10. Volumetric proportions of cement and dry fine and dry 
coarse aggregates in real mix of 1:5.5 were: 
fee 5.5 X 0.382 5.5 X 0.68 
mes00. ©. 0.865 


11. Volumetric proportions of the field mix were: 
109 X 2.03 103 X 4.32 
a ess.a! 96 


say a 1:2.50:4.65 mix. 

12. Net amount of water, per sack of cement, to be added to 
the mix was found as follows: 

This net amount of water equals the amount required for 
strength (water-cement ratio) minus the amount in the aggregate 
plus the amount absorbed by the aggregate. 

Amount required for strength = 7.5 gal. per sack of cement. 

Amount contained in aggregates 


= 1:2.03:4.32 


= 1:2.51:4.64 


= amount in sand plus amount in stone 

= 2.50 X 88.3 X 0.035 + 4.65 X 96 X 0.02. 
= 7.73 + 8.93 = 16.66 lb. 

= 2 gal. per sack of cement. 


Amount absorbed by aggregates 


= amount absorbed by sand plus amount absorbed by stone 
= 2.50 X 88.3 X 0.01 + 4.65 X 96 X 0.01 

= 2.21 + 4.47 = 6.68 lb. 

= 0.80 gal. per sack of cement. 


Net quantity of water to be added to mix 
= 7.50 — 2 + 8.80 = 6.30 gal. per sack of cement. 


13. A small batch of concrete in the given proportions was 
mixed and, when tested, gave a slump of 714 in., which was 
satisfactory. 

14. The mix did not appear to be too harsh for the work in 
question. 

15. Strength tests were made, which gave a unit compressive 
strength of 1085 lb. per sq. in. at an age of 7 days. The time did 
not permit the making of the 28-day strength tests. 

The proportioning of the mix was considered as satisfactory. 


Exercises.—Using the same aggregates and making similar assumptions, 
design a concrete mix to have a slump of from 3 to 4 in., and to give a 


46 CONCRETE PRACTICE 


28-day compressive strength of 2000 lb. per sq. in. Assume that the 
working conditions in the field may not be very good so that Curve B of 
Fig. 3 applies. 


JOB 10. CONSISTENCY OF CONCRETE 


The consistency of the concrete should be such that the mix 
will be plastic and workable. The concrete should work readily 
into the corners and angles of the forms and around the reinforce- 
ment without excessive rodding, tamping, or spading. For 


4 

% i : Proper consistency for rrass CONCTEPE, 
90 & yA ANN asertrn Lighwa Daremenee ere 

Ha YTS Xh\ 

Sy VFM OY 
80 SN : \\_ tb 7is range of consistency should 
OTS iy \| 4¢ used for cast products remrorce: 
DB 1 y coricrere, erc;thin (ernmlers regiuive 

70|> ‘ the greater arri0urr of wares 


[4 


TR 
a eae With this consistency abour 
< : ipa the strenari? lost 
ti Nee 
Ll | Se 
Ba ea 


ThI$ COrSISTEn. 
made corncrere 


ow 


With thesloppy’concrere sore = 
times used i Toad work and 177 
building constructor, two-thirds 
to three-fourths of the possible 
strength of the concrete 15 lost: 


Percent of Maxirnum Stren. 


70 80 90 100 10 120 130 140 150 [60 170 180 190 0 
Water Used- Figures are percent of Quantity Giving Maximum Strength. 


Fia. 8.— Effect of quantity of mixing water on strength of concrete. (Abrams.) 


different kinds of work, different consistencies will be needed. A 
comparatively dry mix would be suitable for heavy foundations, 
while a much wetter mix would be needed for reinforced concrete 
columns and thin wall partitions. The mix should not be so wet 
that free water will collect on the surface. 

The rule in the field should be to use as little water as possible 
and yet have a workable concrete mix. A comparatively slight 
increase in the amount of water will invariably cause a decided 
decrease in the compressive strength of the concrete. On some 
jobs where very wet mixes are used, the resulting compressive 
strength of the concrete may not be more than 50 per cent of 


PROPORTIONING, MIXING, AND PLACING CONCRETE 47 


what it would have been if the amount of mixing water had been 
restricted to the minimum amount needed for workability. 
Professor Abrams has shown conclusively the effect of varying 
the amount of mixing water in a concrete mix with the propor- 
tions of cement and aggregate remaining the same. ‘The results 
of his investigations are shown in a graphical form in Fig. 8. 
The ‘‘slump test”’ is recommended by the Joint Committee in 
their 1924 Report for measuring the consistency or flowability of 
a concrete mix (see Appendix 7). In this test, the tendency of the 
concrete to ‘‘slump,” or reduce its height due to gravity action, 
is measured. ‘The original height of the molded specimen (12 in.), 
minus the height (in inches) after subsidence, gives the slump in 
inches. An increase in the amount of mixing water will increase 
the slump, and vice versa. If a certain quantity of water is 
required for a consistency giving a slump of 14 to 1 in., an addi- 
tion of 10 per cent more water will give a slump of 8 to 4 in., 25 
per cent of 6 to 7 in., and 50 per cent of about 10 in. 
The following specifications for consistency are taken practi- 
cally verbatim from the 1924 Report of the Joint Committee: 
The quantity of water used shall be the minimum necessary to produce 
concrete of a workability required by the engineer. The consistency 
of the concrete shall be measured by the slump test described in the Tenta- 
tive Method of Test for Consistency of Portland Cement Concrete (Serial 
Designation—D138-25T) of the American Society for Testing Materials 
(Appendix 7). The slump for the different types of concrete shall not be 
greater than those authorized by the table which follows, unless authorized 
by the engineer. The consistency shall be checked from time to time during 
the progress of the work. 


WoRKABILITY OF CONCRETE 


Maximum 


Type of concrete Sa aie: 


Ul centre Se a ee 3 
Reinforced concrete: 


a. Thin, vertical sections and columns............... 6 

RISD CSS TSS ie ee 

c. Thin, confined horizontal sections................. 8 
Roads and pavements: 

Fo eta Ye CLCYORTN O's SS RS ir 3 

PRIME STREP IVIOUICULS 55% 2 -9> ops ose cas anne ae os 8 ae 1 


eerie MIO OT INIA: © sii o ace bee wine ooo oo aes wee eee et 2 


48 CONCRETE PRACTICE 


Exercises—Why should a wetter mix be used for thin concrete sections as 
reinforced concrete columns than for heavy concrete sections as massive 
foundations? 

Briefly describe the method used in the slump test to determine the 
consistency of a mix of concrete. 


JOB 11. MEASURING CONCRETE MATERIALS 


There are two ways of measuring concrete materials in use at 
the present time: by volume, and by weight. The common way 
of measuring concrete materials by volume is to measure the 
cement by the sack (assuming that one sack of 94 lb. of cement 
equals | cu. ft.), and the fine and coarse aggregates loose, as they 
are thrown into the wheelbarrows or hopper of the mixer. Usually 
no correction is made for the water content of the aggregate, or 
the bulking effect of water in the fine aggregate. ‘The consistency 
of the mix is left to the judgment of the mixer operator. Batches 
made by this method will usually vary greatly as to their volu- 
metric proportions and consistency. 

If the aggregates are dry and are carefully measured in measur- 
ing boxes or hoppers, the proportioning will be more satisfactory. 
When the fine aggregate (sand) contains some moisture, the bulk- 
ing effect of this moisture in the sand must be allowed for. If 
allowance is not made, this bulking effect may cause an error as 
large as 25 or 30 per cent, when measuring the sand. A variation 
of 2 per cent, for example, in the moisture content, may cause a 
variation of about 10 per cent in the volume of the sand. It is 
very difficult to correct for this bulking effect, when the sand 
comes to the mixer with a varying moisture content. 

The consistency of the mix may be controlled by slump tests 
made on the job. The water tank of the mixer should be so 
devised that the correct amount of water may be added to each 
batch. An automatic attachment (which can be set and locked) 
on the water tank of a mixer of large capacity is essential. 

The best way of measuring concrete materials by volume in the 
field is to measure cement by the sack, the coarse aggregate loose, 
by the use of a measuring box or hopper, and the fine aggregate 
and water together, by the inundation method. It has been 
shown by tests that the bulking effect of water in fine aggregate is 
practically negligible, or very small, when the fine aggregate is 


4 
: 
: 


PROPORTIONING, MIXING, AND PLACING CONCRETE 49 


completely inundated by water. Therefore, if the volume of the 
fine aggregate is measured when it is covered by water, very uni- 
form results will be obtained. After the correct amount of water 
has been determined for any mix, this water may be placed in a 
water-tight hopper and the fine aggregate then added. 

Concrete materials may be measured very easily and accurately 
by weight by using hoppers with automatic scales. A correction 
must be made for the water content of the aggregates, not so 
much for the effect in the quantity of aggregates used as for the 
effect of this water content in the water-cement ratio of the batch. 
The water content of a batch should never vary more than }4 gal. 
(about 2 lb.) per sack of cement in any particular batch. 

All methods of measuring concrete materials have their advan- 
tages and disadvantages, when used on the job, and no method 
yet discovered is ‘‘foolproof.”’ Probably the methods of measur- 
ing the concrete materials by weight and by volume, with the 
sand inundated, are the two best methods yet devised for large 
jobs, especially when the consistency is checked rather frequently 
by the slump test. The moisture contained in the aggregates is 
the most troublesome factor in the correct measurement of con- 
crete materials. 


Exercises—Name some advantages and disadvantages of measuring 
concrete materials by: 

1. Volume with cement by the sack, fine and coarse aggregates loose 
in barrows or hoppers, and water in a tank on the mixer. 

2. Volume with cement by the sack, coarse aggregate in a measuring box 
or hopper, and water and fine aggregate together with fine aggregate 
inundated. 

3. Weight with cement by the sack or pound, and with the fine and coarse 
aggregates and water in hoppers having automatic scales. 

Given, concrete materials with the following unit weights: cement, 94 Ib. 
per cu. ft., sand, 108 lb. per cu. ft., and crushed stone, 97 lb. per cu. ft.: 
(1) Find the proportions by weight of a 1:2:4 mix by volume; and (2) find 
the proportions by volume of a 1:2:4 mix by weight. 


JOB12. COMPUTING QUANTITIES OF MATERIALS FOR CONCRETE 


The present specifications (1924 Report of the Joint Committee) 
state that the unit of measurement for concrete mixes shall be 1 
cu. ft., and that 94 Ib. of cement (one sack or bag or 14 bbl.) shall 
be considered as 1 cu. ft. 


50 CONCRETE PRACTICE 


The following approximate rule may be used in computing the 
quantities of materials required for 1 cu. yd. of concrete. The 
proportion of cement, c, is taken as unity. 

Sacks of cement per cubic yard of concrete 

42 

ae c+st+q 
Cubic yards of fine aggregate per cubic yard of concrete 
aly os ee 
CTs 24 

Cubic yards of coarse aggregate per cubic yard of concrete 

Ey Te lbo.xX 9 0X9 

e+s-+g Pa 

When c, s, and g are the proportions by volume of cement, fine 
aggregate, and coarse aggregate, respectively. 

If the proportions by volume are for cement and mixed (com- 
bined) aggregate, take the volume of the mixed aggregate equal 
to the volume of the concrete, and base the volume of cement on 
the volume of the mixed aggregate; that is, in a 1:6 mix by 
volume of cement to mixed aggregate, 1 cu. yd. of mixed aggre- 
gate and 27 or 4.5 sacks of cement will be required for 1 cu. yd. of 
concrete. This rule will give slightly excessive quantities on 
large jobs, because of the bulking effect of cement and water 
when they are added to the mixed aggregate. 

In volumetric proportioning, the amount of water is usually 
given as gallons of water per sack of cement. The water may be 
measured in a tank calibrated to read to the nearest tenth or 
quarter of a gallon. Sometimes the water tank is graduated to 
read in cubic feet. A U.S. gallon of water contains 231 cu. in., 
and there are approximately 7.5 gal. per cu. ft. 

The computations required, when proportioning concrete 
materials by weight, are quite easy and simple. For example, in 
a 1:3:6 mix by weight, there would be 1 Ib. of cement for every 
3 lb. of fine aggregate and every 6 lb. of coarse aggregate. In 
order to change cubic feet of concrete to pounds of concrete, 
multiply the number of cubic feet by 145 (the approximate weight 
per cubic foot of good concrete). 

The rule which follows may be used when computing weights of 
material per cubic yard of concrete (assuming a cubic yard of 


PROPORTIONING, MIXING, AND PLACING CONCRETE 51 


concrete to weigh 40001b.). The proportion of cement, c’, is taken 
as unity, and c’, s’, and g’ are the proportions by weight of cement, 
fine aggregate, and coarse aggregate, respectively. 

Sacks of cement per cubic yard of concrete 


=e 42.5 

et 
Tons of fine aggregate per cubic yard of concrete 
Bui oe 2s’ en eS. 


fete g «§©=©6 621.25 

Tons of coarse aggregate per cu. yd. of concrete 
29’ = ct x q’ 

e+e’ +a’ 21.25 

To reduce sacks of cement to pounds, multiply by 94. 

The water is usually weighed when proportioning by weight, 
and the amount of water may be given as pounds of water per 
pound of cement or pounds of water per sack of cement. One 
U.S. gallon of water may be considered as weighing 8.35 lb. 


=G! = 


Exercises—Compute quantities of water (gallons), cement (sacks), sand 
(cubic yards), and gravel (cubic yards) for a job requiring 173 cu. yd. of 
concrete of a 1:1.9:3.3 mix by volume with a water-cement ratio of 1.10. 

Compute quantities of water (pounds), cement (sacks), sand (tons), and 
stone (tons), for a job containing 124 cu. yd. of concrete of a 1:2.7:4 mix by 
weight with a water-cement ratio of 1.20. 


JOB 13. HAND MIXING OF CONCRETE 


The mixing of concrete by hand will give good results, if care- 
fully and thoroughly done. This method of mixing is not 
economical except for very small jobs, where only a few batches 
are needed. The batches in hand mixing should be small, prefer- 
ably less than 1 cu. yd., and of such size that all the concrete in 
any one batch can be placed in less than 14 hr. (before initial set 
occurs). 

The tools used in hand mixing are a water-tight metal or 
wooden platform, two shovels, measuring boxes for materials, and 
pails for measuring water. If the batch is small and only one 
man is available for mixing, an ordinary mortar box and a hoe can 
be used in place of the platform and shovels. The mixing plat- 
form should be about 7 X 12 ft. or larger in size, and should be 


52 CONCRETE PRACTICE 


made of tongued and grooved plank, 2 in. thick, tightly and 
securely nailed on 2- X 4-in. joists spaced about 2 or 3 ft. apart. 
The platform should have a 2- X 2-in. strip nailed around the 


(a) Measuring box of one cubic foot (b) Measuring box of four cubic feet 
capacity. capacity. Inside dimensions are: 
length, 36 in.; width, 16 in.; and height, 

12 in: 


Fic. 9.—Measuring boxes. The measuring boxes have neither top nor bottom, 
and may easily be made of one-inch planed lumber. 


Fic. 10.—Convenient portable mixing platform. The platform should be 
made of 2-inch planks planed on one side, preferably of tongue-and-grooved 
material. The finished platform should be watertight and kept as nearly level 
as possible while mixing, to prevent the loss of water, which would carry off 
cement from the mixture. The platform should be equipped with skids or run- 
ners, so that it may be easily dragged to any desired location. <A platform 12 
ft. by 7 ft. will be found satisfactory for ordinary work. Concrete should never 
be mixed except upon a smooth, clean, watertight surface. 


edges to keep the water and mortar from flowing away. ‘The 
platform should be large enough to hold the batch and the two 
workmen who do the mixing. The depth of the measuring boxes 


PROPORTIONING, MIXING, AND PLACING CONCRETE 53 


should be 1 or 1/4 ft. rather than 60r8in. The shovels should be 
short, flat, and square pointed. A No. 2 shovel is satisfactory. 
In mixing a batch, the mixing platform is leveled in a conven- 
ient place, and the fine aggregate is measured and placed on the 
mixing platform in a flat pile. The cement is evenly spread over 
the top of the fine aggregate. This may be done by taking a 


ganas 
HR 


\ 
Ay 


Fig. 11.—Simple tools for making and placing concrete. Water barrel and 
bucket; steel pan wheelbarrow for handling dry aggregate and concrete; sand 
screen for proper grading of aggregates; square pointed shovel for turning and 
mixing concrete; cast-iron concrete tamper for packing concrete; and wooden 
float for finishing. 


sack of cement by the ‘‘ears”’ and letting the cement flow from 
the sack as the workman walks backward, by the fine aggregate. 
The empty cement sacks should be laid aside and counted at the 
end of a day’s work. The used cloth sacks are bundled (tied) in 
groups of fifty, and sent to the cement company which gives 
credit for all good sacks returned. Then two workmen mix the 


04 CONCRETE PRACTICE 


cement and fine aggregate by turning the mix two or three times, 
until the material is of a uniform color. In this work, the two 
workmen stand facing each other at one end of the pile. They 
work their shovels close to the platform diagonally towards each 
other, turning the shovels when they meet. ‘There is a knack to 
this shovel work, which may be acquired by experience. If the 
batch is large, two men can start at each end of the pile and work 
towards the center. 


1S 


S 
SSS 


Upper left: A bundle of 50 cement sacks laid out flat with two ropes 40 in. 
long under the pile, and with a longer rope of about 8 ft. resting on top. 

Upper right: The first operation in bundling is to bring two of the ropes over 
the pile, as shown, tying tightly. 

Lower left: After the short ropes have been tied, the bundle is turned over, 
and the long rope brought around and crossed in the middle of the bundle, 
engaging first the shorter ropes. 

Lower right: Bundle of 50 cement sacks tied and tagged ready for shipment. 


After the cement and fine aggregate are mixed, the mass is 
leveled off and the coarse aggregate measured, wetted, and spread 
over the pile. The batch is again turned two or three times, and 
then ‘“‘troughed”’ or “‘ditched”’ in the center, and the mixing 
water added. This water should be carefully measured in pails, 
so that the same amount can be used for each batch of the same 
size. The dry materials are turned into the water, care being 
taken to prevent the escape of any water. After the materials 


PROPORTIONING, MIXING, AND PLACING CONCRETE 55 


have been turned into the water, the whole batch is turned until 
it appears to have a uniform consistency. Usually about five 
turnings are required for thorough mixing, but most workmen 
stop with two or three turns. The mixing platform and tools 
should be washed clean at the end of the job or of the day’s work. 

When one man does the mixing, the dry materials can be 
thoroughly mixed with a hoe in a mortar box, after which the 
water is added and the mass thoroughly mixed again. 

Correct proportioning and thorough mixing are essential to 
hand mixing. Excess water may mean less strength, more voids, 
laitance, possible washing away of the cement, and perhaps 
separation of the aggregates in the forms. Too little mixing 
means less strength, non-uniformity of consistency, and harsh- 
working concrete. The remixing or retempering of concrete that 
has partially hardened should not be permitted, even if more 
cement is added. 


Ezxercises.—Why should the mixing platform be water tight? 
Why should the measuring boxes be comparatively deep instead of 
shallow? 


JOB 14. MACHINE MIXING OF CONCRETE 


Machine mixing of concrete is usually much better, quicker, 
and more economical than hand mixing, and should be required 
when the amount of work is sufficient to make machine mixing 
economical. In several types of mixers all of the materials are 
placed in the mixer at once; while in some types the dry materials 
are mixed before the water is added. The time required for 
mixing depends on the type, speed, and condition of the machine, 
and varies for different machines. Most machines are designed 
to mix the materials in about 1 min. 

There are two kinds of machine mixers, continuous and batch. 
The continuous mixer is rarely used, because the batch mixer 
gives easier and better control of the proportions and mixing. 
In a batch mixer, a batch of materials is added (or charged) to the 
machine, then mixed and discharged, and the cycle repeated for 
succeeding batches. Most of the batch mixers in use have 
revolving drums with fixed blades inside, though a few types have 
a fixed drum with moving paddles or blades. The drums may be 
shaped like cylinders, double cones, or cubes. The capacities of 


56 CONCRETE PRACTICE 


the drums vary from about 10 to 45 cu. ft. of dry materials and 
from 7 to 30 cu. ft. of wet concrete. The mixing is done by mov- 
ing paddles or blades, or by the rotation of the drum, the mate- 
rials being raised, cut, and turned. 

The mixers are usually charged by means of a lifting skip in 
which the dry materials are placed in the correct proportions. 
Some types of large mixers have overhead bins with spouts. 
The water is added from a tank, preferably an automatic one, 
usually placed over the mixer. After the batch is mixed for 
about 1 min., it is discharged and another batch placed in the 
mixer. ‘The time of mixing should not be less than 1 min. Mix- 


Fig. 13.—Small concrete batch mixer with parts labeled. 


ing for a longer time, even up to 30 min., will not harm the con- 
crete. The concrete may be discharged by tilting the drum or by 
means of a spout. Hither method is satisfactory, though the 
spout is preferred for large mixers. 

The speed of the drum is important. If it rotates too fast, the 
materials will tend to be held next to the rim, while if the speed 
is too slow, thorough mixing will not be accomplished in the 
usual time. A peripheral speed of about 200 ft. per min. is 
satisfactory. 

At the end of the work or of each day’s run, the mixer should 
be thoroughly washed and cleaned out. Any caked concrete 
adhering to the drum or blades should be broken loose and 
removed. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 57 


The materials used must be carefully and accurately measured, 
if consistent results are to be obtained. The cement may be 
measured by the sack. The aggregates should be measured in 
measuring boxes, bins, or barrows, which are comparatively deep, 
rather than shallow, and which allow the material to be leveled 
off easily. Measuring aggregates by the shovelful should not 
be permitted. Weighing of aggregates is usually done fairly 
accurately. The water may be measured in a tank, or weighed. 


Fic. 14.—Concrete batch mixer, 


The following specifications for concrete mixing are taken from 
the 1924 Report of the Joint Committee: 


Specifications for Mixing of Concrete.—The mixing of concrete, unless 
otherwise authorized by the engineer, shall be done in a batch mixer of 
approved type, which will insure a uniform distribution of the materials 
throughout the mass, so that the mixture is uniform in color and homogene- 
ous. The mixer shall be equipped with suitable charging hopper, water 


08 CONCRETE PRACTICE 


storage, and a water-measuring device, controlled from a case which can be 
kept locked, and so constructed that the water can be discharged only while 
the mixer is being charged. It shall also be equipped with an attachment 
for automatically locking the discharge lever until the batch has been mixed 
the required time after all materials are in the mixer. The entire contents 
of the drum shall be discharged before recharging. ‘The mixer shall be 
cleaned at frequent intervals while in use. The volume of the mixed 
material per batch shall not exceed the manufacturer’s rated capacity of the 
mixer. 

The mixing of each batch shall continue not less than 1 min. after all the 
materials are in the mixer, during which time the mixer shall rotate at a 
peripheral speed of about 200 ft. per min. 

When hand mixing is authorized by the engineer, it shall be done on a 
water-tight platform. The cement and fine aggregate shall first be mixed 
dry, until the whole is of a uniform color. The water and coarse aggregate 
shall then be added, and the entire mass turned at least three times, or until 
a homogeneous mixture of the required consistency is obtained. 

The retempering of concrete or mortar, which has partially hardened, 
that is, remixing with or without additional cement, aggregate, or water, 
will not be permitted. 

Exercises.— What are the three atie or steps of the mixing cycle? Why 
is a batch mixer usually better than a continuous mixer? 


JOB 15. CONCRETING PLANT 


The fundamental principle in the design of a concreting plant 
is to select, arrange, and use the men, machinery, and materials 
so that the work will be done in the most efficient manner, espe- 
cially in regard to costs. 

The first thing to do is to examine the site, noting the location 
of the structure to be built and the space available for the con- 
crete plant. The topography of the ground has some effect on 
the plant layout, in that materials preferably should not be 
moved uphill, and that the force of gravity may be sometimes 
used if the site is sloping. 

The total yardage to be placed, the time limit for the job, time 
of year, method of delivering materials to job, available storage 
space, water supply, etc., all must be considered in the selection of 
the machinery and in the plant layout. 

The size of the mixer selected depends upon the total yardage 
to be placed, and the time limit for this part of the work. Due 
allowance must be made for time required for installation and 


PROPORTIONING, MIXING, AND PLACING CONCRETE 59 


removal, and for delays from various causes. In general, it may 
be assumed that the mixer will be working only about half of the 
working hours available. 

The method used in getting the materials to the mixer is 
important. If the storage space is ample, comparatively large 
piles of coarse and fine aggregates may be placed near the mixer 
(the coarse aggregate should be closer, as it is larger). The 
cement should be stored in a weather-tight shed. If the storage 
space is small, it may be necessary to have the materials stored 


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Fig. 15.—Small concrete plant layout. 


elsewhere and hauled to the mixer by trucks. Care must be 
taken to keep dirt and other impurities out of the aggregates. 
If necessary, the mixing plant could be placed elsewhere, and the 
mixed concrete hauled to the work in trucks. 

Efficient operation of the mixer is necessary for economical 
work. The time required for loading will vary from 10 sec. to 1 
min., with an average of about 20 sec. The time of mixing should 
never be less than 1 min., though many mixer operators try to 
gain time by reducing the time of mixing. The time required 
for unloading requires from 10 sec. to 1 min. with an average of 


60 CONCRETE PRACTICE 


30 to 35 sec. Thus the total time required for a mixing cycle 
varies from about 114 to 3 min. with an average of about 2 min. 
Of course, it is improbable that a batch every 2 min. could be 
produced hour by hour and day by day, due to delays in getting 
the materials to the mixer, delays in placing the mixed concrete, 
and delays due to breakdowns of some part of the plant. 

The apparatus for measuring the materials (cement, fine and 
' coarse aggregates, and water) for the batch must be such that the 
materials can be accurately and quickly measured and the 
correct proportions of the mix provided in all cases. 


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Fic. 16.—Large concrete plant layout. 


The concrete coming from the mixer may be transported to the 
forms in one of five ways. No matter which method is chosen, 
it should have a capacity equal to, or a little greater than, that of 
the mixer, so that the operation of the mixer will not be slowed 
up. The methods referred to are the following: 

1. By barrows or carts, in which the concrete is wheeled from 
the mixer to the forms. A tower and a hoist may be used for 
raising the carts and barrows to higher levels. 

2. By a tower and spouting system, where the concrete is 
discharged into a skip or bucket, and this skip hoisted up a 


tower and dumped into a hopper, from which the concrete flows 


through spouts to its place in the forms. 


ee 


PROPORTIONING, MIXING, AND PLACING CONCRETE 61 


3. By use of cableways and large buckets (either tilting or 
bottom dumping), to carry the concrete to the place of deposition. 

4. By a bucket or spout attached to the machine (as in a 
large paving mixer), by which the concrete is placed in position. 

5. By use of a belt conveyor to carry the concrete to the forms. 

In general, no set rules may be given for the design of a con- 
crete plant for any particular job. For some jobs one design is 
easily seen to be the best, while for other jobs two or three designs 
may be suitable. Sometimes, one large mixer is preferable to 
two or three small ones, and vice versa. No matter what design 
is selected, the plant should be well balanced as to crew, material 
supply, mixing capacity, and concrete transportation and 
deposition in forms. 

When computing the total cost of a given plant on any job, the 
following items should be considered: (1) cost of plant; (2) cost 
of installation, including freight and transportation costs; (3) 
cost of operation; (4) cost of maintenance; (5) cost of removal: 
(6) depreciation; and (7) interest on investment. 

The figures accompanying this job show examples of plant 
layouts for a small and a medium-sized job. A study of these 
plans will show how the general details of the plant layouts were 
handled. 


Exercises.—State the general principle of concrete plant design. What is 
meant by balanced design of a concreting plant? Draw a sketch showing a 
plant layout for concreting a basement wall. 


JOB 16. TRANSPORTATION OF CONCRETE 


The transportation system must be so designed and operated 
that the concrete will be carried from the mixer to the forms 
before the initial set has occurred; that no part of the concrete will 
be lost in transporting; that no segregation of the materials will 
take place; that the delivery of the concrete be fairly continuous 
and uninterrupted; and that the work of transporting the con- 
crete will be efficiently, rapidly, and economically done. The 
choice of a transportation system depends on the particular job 
and, in some instances, on the plant available. 

Some of the methods of transporting concrete are shovels, 
chutes, wheelbarrows, carts, cars, auto trucks, buckets and cable- 
ways, belts, pipes, spouts and spouting plants (including hoists, 


62 CONCRETE PRACTICE 


buckets, bins, pipes, spouts, etc.). A hoisting plant may also 
be used with barrows and carts. : 
On very small jobs, the concrete may be shoveled, chuted (in 
wooden chutes), or carried in wheelbarrows from the mixer to the 
forms. 
On larger jobs (such as reinforced-concrete factory and office 
buildings, etc.), the use of special barrows holding about 2 cu. ft., 


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or two-wheeled carts holding about 5 or 6 cu. ft., will be economi- 
cal. A hoisting tower may be used to hoist the carts from the 
mixer level to the different floors, or the conerete may be hoisted 
in buckets and dumped into a bin at the floor level, the carts being 
loaded at the bin. Double runways must be provided for the 
carts so that they can pass. These runways should be of plank, 
and should be moved about (or taken up) as the work progresses. 
The hoisting towers are usually built of wood to meet the needs 
of the particular job. The method of transporting concrete with 


PROPORTIONING, MIXING, AND PLACING CONCRETE 68 


carts is usually economical, and hence should always be con- 
sidered when selecting the transportation system. 


Capeessiet® 


Fig. 18 


Bos 


.—Typical boom plant installation. 


Fic. 19.— Measuring barrow. 


Small dump cars running on tracks with 15- or 20-lb. rails have 
been used on jobs where the forms are located some distance 
from the mixer, as in road or tunnel work. 


64 CONCRETE PRACTICE 


Large auto trucks have been successfully used to transport the 
concrete from a central mixing plant to the job when the avail- 
able space at the site is not large enough for a complete concreting 


Fia. 20.—Barrow for transporting concrete. 


plant, or when it is desired to have the concrete mixed at a central 
plant, where the proportioning and mixing can be more scientifi- 
cally controlled. 


Fia. 21.—Cart for transporting concrete. 


In the spouting system, the concrete is hoisted from the mixer 
and discharged into a small bin or hopper on the hoisting tower. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 65 


The concrete flows from this bin through metal chutes or spouts 
to the forms. The slope of the spouts should not be less than 1 
vertical to 2 horizontal for ordinary work. The consistency of 
the concrete, and the slope of the spout or chute should be such 
that the concrete will flow evenly and uniformly, without any 
stoppages or segregations of materials. The spouts or chutes 
may be supported by suspension cables, booms, or tripods, or 
combinations of these three. The tripod method of support is 
usually limited to short distances (about 50 ft. or less), and is 
often used to extend the length of the cable or boom chutes. The 
boom system may be used up to about 200 ft., after which the 


Fig. 22.—Tilting bucket. Fig. 23.—Bottom dump bucket. 


suspension cable system is better. Chutes suspended from a 
cable can be used for transporting concrete most any distance, by 
adding extra hoisting towers as they are needed. Hoisting 
towers are usually constructed of steel up to heights of about 
200 ft. 

The suspension cable and bucket system has been used on 
large jobs, such as dams. In this system, the bucket of concrete 
is carried by a suspended cableway to the forms which are to be 
filled. The system must include a method of raising, lowering, 
and dumping the buckets. Both tilting and bottom-dumping 
buckets have been used. 

Belt conveyors have been satisfactorily used on some jobs, such 
as long sewers, where it is difficult to transport the concrete by 
other methods. 


66 CONCRETE PRACTICE 


In such work as lining tunnels, a pneumatic system is essential. 
The concrete is forced through the pipes, by air pressure, into 
places and crevices where it is practically impossible to deposit 
it by other means. 


Exercises.—Name four different methods of transporting concrete. 
With the aid of sketches, describe a transportation system for concrete 
using a hoisting tower and carts, or a hoisting tower and spouts or chutes. 


JOB 17. DEPOSITING CONCRETE IN FORMS 


Careful deposition of concrete in the forms is very important, 
as no faults in the mix or in the placing can be corrected later. 
Before starting to mix and pour concrete, the mixer and trans- 
porting system should be thoroughly cleaned, and all old concrete 
and foreign materials should be removed from the inner surfaces 
of the equipment. Any dirt or other debris should be removed 
from the forms in which the concrete is to be placed, and the 
surfaces of the forms thoroughly wetted (except in freezing 
weather) or oiled. 

Concrete should be transported from the mixer as rapidly as - 
practicable, without loss of materials or segregation. ‘The time 
required for transporting and depositing should not be more than 
30 min. The flow of the concrete from the mixer to the forms 
should be continuous, until the particular section of the forms 
has been filled. It is advisable to keep the surface of the con- 
crete approximately horizontal in wall, column, or footing forms, 
while the junction plane in beams or slabs should be nearly 
vertical. 

After the concrete has been deposited in the forms, it should be 
thoroughly compacted. The tools used are shovels, spades, 
forks, rods, tamping bars, etc. Spading the concrete next to the 
form surface tends to make a smooth surface without air pockets. 
The concrete must be thoroughly worked into the corners of the 
forms and around the reinforcement. Tamping and rodding 
tend to remove air voids, and increase the density and strength 
of the concrete unless the mix is sloppy, in which case too much 
tamping may tend to cause a separation of the materials. The 
compacting of concrete in thin forms may be helped by hammer- 


ing the outside of the forms opposite the freshly deposited 


concrete. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 67 


Retempered or remixed concrete or mortar that has eS 
its initial set should not be placed in the forms. 

The concrete, when deposited, should have a temperature 
between 40 and 120°F. In freezing weather the temperature of 
the concrete should not be permitted to fall below 50°F. for 72 
hr., or until the concrete has thoroughly hardened. 

Construction joints should be made only at the places shown 
on the plans. Whenever it is necessary to introduce other 
construction joints, the plans and design of such joints should be 
approved by the engineer. Construction joints in columns 
should be horizontal, and should be located at the under side of 
the floor or column capital, while the construction joints in floors 
and beams should be vertical and located near the center of the 
span. . 

Exercises.—Why should the forms be wetted or oiled before concrete is 
placed in them? 

What is the object of tamping freshly placed concrete? 

How much time is permitted for the transportation of the concrete 
from the mixer and the placing of the concrete in the forms? 

In general, where should the construction joints be located? 


Why should fresh concrete be kept at a temperature of 50°F. or more for 
72 hr., or until it has thoroughly hardened? 


JOB, 18. BONDING NEW CONCRETE TO OLD 


When new concrete has been deposited on or against old con- 
crete that has set, care must be taken to secure a good bond. 
Perhaps the best method (and the most common one) is to chip 
the surface of the old concrete so as to roughen it and expose the 
coarse aggregate, and then thoroughly to clear away all loose 
material. The exposed surface should be thoroughly wetted with 
water, and a thick, neat cement grout added. Fresh concrete 
should be placed against the surface, before the grout has 
obtained its initial set. This method will practically always 
produce a good bond between the new and old concrete. 

Some companies have made and placed some patented chemical . 
compounds on the market, which are guaranteed to give a good 
bond between old and new concrete. 

Exercises.—Why should the surface of the old concrete be chipped and 
cleaned? 

What is the object of wetting the exposed surface? 

What is the object of adding a neat cement grout? 


68 CONCRETE PRACTICE 


JOB 19. PROTECTION OF CONCRETE WHEN HARDENING 


After the concrete has been placed, it must be allowed to 
‘‘cure”? or harden. This hardening process is a rather slow 
chemical process, in which the cement and water unite to form 
compounds which give strength and durability to the concrete. 
In order that this hardening process may go on to the best 
advantage, the fresh concrete, for from about 3 days to a week, 
must be protected from shocks, excessive vibrations, loads, 
extreme heat, cold and freezing temperatures, too rapid drying 
out, and from contact with any impurities which may retard, 
stop, or destroy the chemical action. 

Fresh concrete, which is almost entirely enclosed in forms 
(walls, for example), requires practically no protection from hot 
weather and dry winds. If much of the concrete surface is 
exposed, as in a concrete pavement, this surface should be pro- 
tected from the hot rays of the sun by a covering such as a tarpau- 
lin. After the concrete has obtained its hard set, it may be 
covered with dirt, sand, water, or canvas until it is a week or two 
old. The covering should be kept wet by sprinkling thoroughly 
at least once a day when necessary. If the water is evaporated 
from the surface before the concrete has had time to harden 
properly, this part of the concrete may be weakened, because not 
enough water will be left to combine with all of the cement. 

In freezing weather, heated materials should be used and the 
fresh concrete kept at a temperature of 50°F. or more, until it 
has time to harden thoroughly (from 3 days to 1 week). ‘This 
subject will be taken up in more detail later on. 

Acids, alkaline solutions, and other strong liquids and oils 
should not be permitted to come into contact with the exposed 
surface of the fresh concrete until the concrete has thoroughly 
hardened. Many of these liquids will penetrate the fresh con- 
crete and retard, and in some instances stop, the hardening 
process. 

In general, the forms should not be removed until the concrete 
has hardened and obtained sufficient strength to carry its loads. 
The time required before form removal may be a week or a month, 
depending on the character of the concrete, weather (temperature), 
loading conditions, ete. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 69 


JOB 20. PLACING CONCRETE UNDER WATER 


Concrete should be deposited in air whenever practicable, 
because the results obtained by depositing concrete under water 
are always more or less uncertain. When, however, the expense 
of depositing in air would not be warranted, concrete may be 
placed under water, provided several precautions are taken in 
the selection of the aggregates, and in the mixing, placing, and 
curing. 

The aggregates used should be free from loam and any other 
material that will tend to cause laitance. Washed aggregates 
are preferred. 

The proportions of the mix should be equivalent to a 1:4 mix 
by volume, or richer. 

The mixing of the concrete should be very thoroughly done, 
and the consistency of the mix should not be too wet. 

The method used in placing the concrete under water should be 
such as to prevent the washing of the cement out of the mix; to 
minimize the formation of laitance and the segregation of the 
materials; to avoid disturbing the concrete previously placed, 
before it has attained hard set; to avoid flow of water through the 
fresh concrete; and to avoid the formation of work planes or layers. 
Fairly tight cofferdams are required in flowing water to prevent 
the washing away of the cement. Pumping should not be per- 
mitted in the cofferdams while the concrete is being placed, and 
until the concrete is thoroughly hardened. The temperature 
of the water should not be less than 35°F. The laitance should be 
thoroughly removed from the surface of the concrete before resum- 
ing work after a delay or stop of any kind. The three methods 
commonly employed are known as: (1) the tremie method, (2) the 
drop bottom bucket method, and (3) the bag method. 

The tremie is a long wooden box or metal tube open at the top 
and bottom. It must be water-tight and large enough to permit 
the free flow of concrete through it. The tremie may be filled by 
placing the lower end in a box of concrete, so as partially to seal 
the bottom, before being lowered in position; or by plugging the 
tremie with sacks which will later be forced down the tremie and 
out by the concrete; or by plugging the end of the tremie with 
sacks of concrete. The tremie must be kept full of concrete 


70 CONCRETE PRACTICE 


during the time the concrete is being placed. The concrete may 
be discharged from the tremie by raising it a little and moving it, 
so that the fresh concrete moves freely and slowly out of the 
bottom. If a charge of concrete should be lost, the tremie must 
be raised and filled again. 

The drop-bottom bucket is one iin a top, which has bot- 
tom doors which open freely downward and outward. The 
bucket is filled level full with fresh concrete, and lowered slowly 
to avoid backwash, until it rests on the surface on which the 
concrete is to be placed. The bottom doors are then opened 
and the bucket raised very slowly until well above the concrete. 

In the bag method, bags of jute or other coarse cloth are filled 
about two-thirds full of concrete, and placed under water by 
hand. The bags should be uniformly laid by “headers” and 
‘“‘stretchers”’ so as to form a compact, interlocked mass. 


Exercises —Name the three common methods used for ceposne concrete 
under water. 

Why is washed aggregate preferred for concrete work of this type? 

Why should a tremie be kept full of concrete at all times during the placing 
of concrete? 

When should comparatively rich mixes be used? 

What would probably happen if water were permitted to flow through the 
concrete before it had hardened? 


JOB 21, CONCRETING DURING FREEZING WEATHER 


Satisfactory concreting may be done in cold weather, if the 
concrete is kept at a temperature of 50°F. or more (not over 
120°F., however) from the time the materials are placed in the 
mixer until the fresh concrete has thoroughly hardened in the 
forms, a period of not less than 3 days. Successful work depends 
upon the following five factors: 

1. The fine and coarse aggregates and mixing water should be 
heated to from 100 to 150°F., before being placed in the mixer. 
The cement may or may not be heated as it forms only a small 
part of the volume of the concrete. 

2. The concrete should be placed in the forms (preferably — 
warmed) immediately after mixing, so that but little of the heat 
will be lost. The concrete should have a temperature of not less 
than 70°F. when placed in the forms. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 71 


3. The concrete should be protected from the cold immediately 
after it is placed in the forms, so as to retain its heat. 

4. The concrete in the forms must be kept at a temperature of 
not less than 50°F. for not less than 72 hr., and until it has 
thoroughly hardened. 

5. The forms should not be removed too soon. It is advisable 
to test the concrete before removing the forms. 

The best method of heating aggregates and water is by the 
use of steam pipes. The aggregates may be placed on top of 
several coils of steam pipes and covered with canvas to keep in 
the heat. The water may be heated by a steam coil in the water 
tank. An old boiler may be economically used to generate the 
steam required. A thermometer should be used to determine 
the temperature of the materials. About 1000 B.t.u. are 
required to heat 1 cu. yd. of materials, 1°F. Aggregates should 
preferably not be heated to a higher temperature than 150°F. 
Steam pipes are excellent for thawing frozen aggregates. Aggre- 
gates containing frozen lumps must not be used until all frozen 
material is completely thawed. 

Another method of heating the aggregates is to use sections of 
an old metal smokestack or culvert. A fire is built on the inside 
and the aggregates are heaped over the top. Care must be 
taken not to heat the coarse aggregate too hot, as a stone heated. 
to about 600°F. will retain much of its heat a comparatively long 
time, and may weaken the concrete by evaporating the water 
on its surface and leaving a thin coating of dry cement. 

As soon as a batch is mixed, it should be removed from the 
mixer and placed in the forms as soon as possible. The tempera- 
ture of the batch in the barrow or cart should be not less than 
80 or 90°F., as shown by a thermometer; or the temperature of 
the batch, when placed in the forms, should not be less than 70°F. 
The forms should be cleaned of all frozen material, and should be 
warmed when the fresh concrete is placed in them. Forms that 
are enclosed in a portion of a building that is heated will usually 
be warm enough. Steam pipes or a stream of hot water may be 
used for heating the forms. 

Immediately after the concrete is placed, it should be protected 
from the cold. Exposed concrete surfaces may be covered with 
panels of light sheathing, tar paper, canvas, tarpaulins, or build- 


72 CONCRETE PRACTICE 


ing paper. Straw and manure are satisfactory, but manure 
should not come into contact with the surface of the concrete. 
When constructing buildings, portions of the building may be 
enclosed by canvas, wooden sheathing, or building paper, and 
the part enclosed, heated by salamanders or steam pipes, so as to 
keep the temperature of all parts of the enclosure above 50°F. 
The number of salamanders needed will vary with the outside 
temperature and the efficiency of the covering. The covering 
material should be kept at least 10 in. away from the outer forms, 


Fic. 24.—Protection of building when concreting during cold weather. 


so that there will be a free circulation of warm air all about the 
outer forms. The protection and heating should be continued 
from 3 to 5 days, depending on weather conditions and tempera- 
tures. Covering an exposed top of a slab with tar paper and 
straw immediately after pouring is a good protection against 
frost. | 

The forms should not be removed in cold weather until there is 
no doubt but that the concrete has thoroughly hardened. ‘The 
concrete may be tested by heating the surface with a jet of hot 
water or steam, or with the flame of a blow torch. If the con- 
crete is frozen, it will soften as the heat thaws the water. If the 


PROPORTIONING, MIXING, AND PLACING CONCRETE 73 


concrete is hardened, the heat will not affect it. Frozen concrete 
frequently looks like hardened concrete, and will often give the 
same ring when struck by a hammer. 

Concrete that has been once frozen before it has attained initial 
set can sometimes be saved by enclosing and heating it. After 
thawing, the concrete will set and harden if kept warm. Con- 
crete that is frozen after setting has started is always damaged to 
some extent. Concrete that has been frozen, thawed, and frozen 
again is practically worthless in regard to strength and durability. 

Common salt, calcium chloride, glycerine, alcohol, and various 
anti-freezing compounds have all been added to the mixing water 
to lower the freezing temperature of the concrete. Nearly all of 
these materials tend to decrease the strength of the concrete, and, 
consequently, should be sparingly used. Concrete hardens very 
slowly at temperatures below 40°F., consequently, it is far better 
to heat the aggregates and water, and keep the concrete at a 
temperature over 50°F. until it has hardened. At 40°F., con- 
crete requires four times as long to harden as at 50°F., and nine 
times as long as at 70°F. 


Exercises.—What are the five essentials to successful concreting in freezing 
weather? 

How hot should the aggregates and mixing water be before being placed 
in the mixer? 

How hot should the batch be just after it is placed in the forms? 

Why should the forms be warmed? 

For how long should fresh concrete be protected in freezing weather? 

What should be the minimum temperature provided? 

How may concrete be tested to determine if it is frozen or hardened? 


JOB 22. MAKING WATERPROOF CONCRETE BY PROPER PROPOR- 
TIONING OF THE CONCRETE MATERIALS 


Results of experiments show that, while it is impossible to make 
concrete actually waterproof, it may be made practically so by 
several methods. While it is difficult to keep out all of the water, 
yet the water may be prevented from passing through the con- 
crete in such quantities as to cause damage and inconvenience. 
Concrete may be made practically water tight against heads of 
water up to about 40 ft. 

In general, the flow of water through the concrete varies 
directly with: (1) the number and size of the shrinkage and 


74 CONCRETE PRACTICE 


temperature cracks; (2) the amount of voids in the concrete (the 
voids may be comparatively large due to imperfect grading of 
the aggregate, excess of mixing water, segregation of materials, 
and improper mixing, placing, and curing); (3) the water pressure 
or head on the concrete; and (4) the amount of laitance. The 
flow of water through concrete varies inversely with the age, — 
density, and amount of cement in the mix. 

It is difficult to control the shrinkage and temperature cracks, 
but these cracks may be reduced in size and number by the use of 
well-graded aggregates, proper consistency of mix, thorough 
mixing, careful placing and compacting of the concrete, proper 
curing, and, in some instances, by the addition of temperature 
reinforcement. Expansion and contraction joints should be 
constructed very carefully. 

The amount of voids in the concrete can be reduced by making 
the concrete more dense. This may be accomplished by using 
good materials, grading the aggregates, properly proportioning 
the cement, water, and aggregates to give the densest concrete, 
correct measuring of materials, thorough mixing, careful placing 
and compacting of the concrete in the forms, protection during 
curing against extremes of temperature and too rapid drying, and 
by using a larger proportion of cement. Proportioning the dry 
materials by the sieve analysis and maximum density curve 
method usually gives a water-tight concrete. In general, a 
slight excess of fine materials is desirable. A mix leaner than a 
1:6 should rarely be used. 

The water pressure or head on the concrete may often be 
reduced by providing outlets for the water at a comparatively low 
level, or by using drainage pipes to carry the water away. 

An excessive amount of laitance (a porous, white, chalky mate- 
rial which often appears on the surface of fresh concrete) may be 
prevented by not using an excess of mixing water, by avoiding 
the use of dusty aggregates, by thorough mixing, by careful 
placing and compacting in the forms, and by avoiding “‘ work”’ 
planes whenever possible. 


JOB 23. WATERPROOFING CONCRETE BY ADDING INTEGRAL 
COMPOUNDS 


The water-tightness of concrete may be improved by adding 
integral compounds in liquid form to the mixing water or in dry 


PROPORTIONING, MIXING, AND PLACING CONCRETE 175 


form to the cement. The object of adding integral compounds 
is to make the concrete more dense, or water repellant, or both. 
In general, this method is not very efficient. A publication of 
the Bureau of Standards (Technologic Paper No. 3) states that: 


The addition of so-called “integral’? waterproofing compounds will 
not compensate for lean mixes, nor for poor materials, nor for poor workman- 
ship in the fabrication of concrete. Since in practice the inert integral 
compounds (acting simply as void-filling material) are added in such small 
quantities, they have very little or no effect on the permeability of concrete. 
If the same care be taken in making the concrete impermeable, without the 
addition of waterproofing materials, as is ordinarily taken when waterproof- 
ing materials are added, an impermeable concrete can be obtained. 


Among the compounds added to the mixing water in a liquid 
or paste form are: an alum soap solution (1 part alum to 2.2. 
parts of soap), chloride of lime, wax, mineral oil residuum, and 
several specially manufactured compounds. As most of these 
compounds tend to weaken the strength of the concrete, large 
percentages should not be used. 

The finely powdered, dry compounds, mixed with the dry 
cement, include lime, puzzolan cement, fine clay, feldspar, finely 
ground sand, and various manufactured substances. An addi- 
tion of 10 per cent of hydrated lime, based by weight on the 
weight of the cement, is recommended by many engineers. 
Finely divided clay in an amount equal to about 5 per cent of the 
fine aggregate has been used in some instances. The addition of 
the lime or clay aids in filling the small voids in the concrete and 
thus making the concrete more water tight. 


JOB 24. WATERPROOFING CONCRETE BY WATERPROOF COAT- 
INGS OR MEMBRANES 


The surface of concrete can be made more water resistant by 
the addition of waterproof coatings or washes, or by layers of 
waterproofing material. 

Among the waterproof coatings commonly applied to concrete 
surfaces are alum and soap mixtures (often known as ‘‘Sylvester 
Process’’); alum, lye, and cement washes; cement grout, with or 
without the addition of a water repellant; paraffines, waxes, or 
other mineral bases applied in a melted condition, or cold in a 


76 CONCRETE PRACTICE 


solution; various varnishes and paints; coatings of common oils; 
special bituminous (tar and asphalt) coatings; and various 
materials prepared by different manufacturers. 

To secure good results, the concrete surface to which the coat- 
ing is applied should be clean, dry, and free from foreign matter. 
The coating should be homogeneous, continuous, uniform, and 
sound. Cracks in the coating will let the water through. All of 
the coatings named, except the bituminous kinds, are usually 
applied to the concrete surface directly exposed to water action. 

The Sylvester Process consists of first applying, by means of a 
soft brush, a boiling hot soap solution made by dissolving 34 lb. 
of soap in 1 gal. of water. After the soap solution has dried 
(which requires about 24 hr.), the alum solution at a temperature 
of about 70°F. is applied with a brush. This alum solution is 
made by dissolving 2 oz. of alum in 1 gal. of water. The tempera- 
ture of the air should not be less than 50°F., and the solutions 
should be well brushed in. ‘This constitutes one treatment, and 
as many treatments may be given as desired. 

Layers of waterproofing materials or membranes may be 
placed on the concrete surface on which the water pressure is 
applied, or else placed between two layers of concrete. ‘The 
concrete surface should be hard, clean, dry, and slightly rough. 
The membrane must be well lapped, so as to be continuous, of ‘as 
many thicknesses as required, and must be protected from injury. 
The several layers of the membrane are usually bound together, 
and to the concrete surface, by some bituminous compound. 

Some of the membranes commonly used are: tarred felt, 
asphalt felt, special felts, burlap, burlap saturated with tar and 
asphalt, and combinations of canvas, felt, and burlap. The 
bituminous materials are: hot asphalt mastic, hot asphalt, hot 
coal tar, and various specially manufactured asphaltic compounds. 

The membranes and bituminous materials should be applied 
as directed by the manufacturers. Joints in membranes should 
be broken at least 12 in., and laps in the membrane should be at 
least 12 in. Each layer of membrane and bituminous material 
must completely cover the surface without cracks or blow holes. 

The following table is taken from ‘‘ Modern Method of Water- 
proofing,” by M, H. Lewis; 


PROPORTIONING, MIXING, AND PLACING CONCRETE 77 


NuMBER OF PLY oF WaTERPROOFING REQUIRED FOR VARYING HEADS OF 


WATER 
Material 
Head 
of water} Coal tar and Commercial Special felts Asphalt mastic, 
asphalt and and com- thickness in 
felt : 
felt | pounds inches 
0 2 2 1 0.25 
1 3 3 2 0.625 
2 4 4 3 0.625 
6 5 5 4 0.625 
8 926 6 5 0.75 
10 7 i 6 0.75 
15 8 8 7 0375 
20 9 9 8 0.75 


Exercises—How many plys (thicknesses) of coal tar and felt would be 
required if the head of water is 12 ft.? 


JOB 25. WOODEN FORMS FOR CONCRETE 


Forms for concrete must be tight, so as to prevent leakage of 
mortar. They must also be properly braced and tied to keep 
their position and shape with no bulging and twisting, and must 
have strength enough to support the concrete and the construc- 
tion loads which may be placed upon them. 

As the cost of the form work equals from 15 to 40 per cent of 
the total cost of a concrete structure, it is worth while to study 
the design of the forms in regard to economy in labor, and in the 
use and re-use of the materials. 

The cost of form lumber depends upon the design of the forms, 
re-use of the forms, replacements required at each set up, and value 
of form lumber at the end of the job. The labor cost of forms 
depends upon the cost of making units and shapes to be used, cost 
of erection, cost of removal (stripping), and cost of handling 
and erection for the next set up 

The following rules should be followed in the design of lumber 
forms: 

1. Use stock sizes and lengths of lumber, and use as few lengths 
as practicable. 


78 CONCRETE PRACTICE 


2. Use as few units as practicable, and do not make them too 
heavy. 

3. Allow for clearances and small inaccuracies. 

4. Provide for easy stripping. 

5. Provide for re-use of such units as panels, beam forms, 
column forms, etc. 

6. Provide bevel cuts and keys, so that forms can be released 
without excessive prying. 

The kind of lumber used for form work should be a partially 
seasoned spruce or pine of almost any variety that is sound and 
free from twists, shakes, knots, and surface decay. Hemlockis 
satisfactory, if it is not to be re-used, as it often weathers rapidly. 
The form lumber selected depends upon price, kind, and quantity 
available in the local market. Partially seasoned lumber is best, 
as green lumber may shrink and kiln-dried lumber may swell. 

For all surfaces where the concrete will later be exposed, only 
dressed lumber should be used. Ship lap is preferable for flat 
work, though tongued and grooved (T and G) and dressed and 
matched (D and M) lumber are satisfactory. The inside sur- 
faces of the forms should be dressed true and free from joint and 
other marks. Corners should be beveled when practical. 

In general, the builder’s knowledge and experience will enable 
him to select the proper sizes of lumber without special computa- 
tions. The horizontal members should support the weight of 
the concrete and other constructions which may be placed on 
them, and the vertical forms should be able to resist a hydrostatic 
pressure of 145 lb. for each vertical foot of height. The sizes of 
lumber frequently used are: 2-in. stock for columns and beam 
and girder bottoms; 1- or 114-in. stock for floor panels and beam 
and girder sides; 1- or 2-in. stock for footings; 2- < 4-in. stock 
(2 X 4’s) for stringers and joints; 3- X 4-in. or 4- X 4-in. stock 
for struts, posts, shores, and uprights; 1- or 2-in. stock for cleats; 
and 1- X 6-in. or 14- X 6-in. stock for cross ties and bracing. 
Dressing lumber reduces its dimensions from 44, to 14 in. for 
for each surface dressed. Common symbols for dressed lumber 
are S18, S1S2E, S28, S48, etc., meaning, surface 1 side, surface 
1 side 2 edges, surface 2 sides, surface 4 sides, etc., respectively. 

The nails used in framing should be numerous and long enough 
to hold the forms together. ‘Too many and too long nails require 


Se 


PROPORTIONING, MIXING, AND PLACING CONCRETE 79 


more labor when stripping the forms and preparing the form 
lumber for re-use. Sizes of nails commonly used are given in the 
table which follows. 


Approximate number 


Sizes in pennies Length in inches per pound 
4 1.50 315 
5 1.75 270 
6 2.00 180 
7 2.25 160 
8 2.50 105 
9 2.75 95 

10 3.00 70 
12 3225 63 
16 3.50 47 
20 4.00 3t 
30 4.25 24 
60 6.00 11 


Whenever practical, nails need not be driven clear in to the head, 
as leaving the head end of the nail projecting a little makes the 
stripping of forms easier. A double-headed form of nail has 
been satisfactorily used for this purpose. 

On the job, the lumber piles, sawmill (if one is used), and 
benches should be arranged for efficient work. Many of the 
units, or parts of units, such as portions of beam and column 
forms, panels, etc., are first prepared on the benches, and later 
erected in the building. Careful planning can save lumber 
and labor in the making, erecting, and stripping of forms. 

For larger jobs, such as large reinforced concrete buildings, the 
drafting office should provide detailed drawings for all forms for 
beams, columns, slabs, etc., as well as some general assembly 
drawings showing how the different forms fit together. Key 
drawings, showing the general arrangement and layout of the 
work, are often required. Such elaborate drawings are not 
needed on small jobs, though the office man or job foreman should 
have rough sketches of the form work when such drawings will 
be helpful. 


80 CONCRETE PRACTICE 


Before the concrete is poured, the interior surfaces of the forms 
should be thoroughly wetted with water, or oiled. Crude oil, or 
a mixture of kerosene and linseed oil, is commonly used. The 
oiling should be done before the reinforcement is placed in the 
forms. If the concrete walls are to be plastered later, the forms 
must be wetted instead of oiled, as plaster will not stick to an 
oiled surface. 

Forms should not be removed until the concrete has set and 
hardened, so that it is strong enough to support the loads. The 
time that the forms should be left in place depends upon the 
temperature and humidity of the air, the loads to be carried by 
the concrete, and, to some extent, on the type of structural mem- 
ber. The following table shows good practice: 


Time REQUIRED BEFORE REMOVING FORMS 


Temperature 


Member Above 60°F. 45 to 60°F. Less than 45°F, 


Required time in days 


Compression members 
such as columns and 


WIS. eos cen en nea 4 to 6 Not less than 10 | Not until tests 
Side forms of beams have been made 

and irdere sc eee 5 to 7 Not less than 10| that show that 
Bottom forms of slabs the concrete has 

Olishortispan lt. oe 6 to 10 Not less than 14| thoroughly 
Bottom forms of beams hardened 

ANG SiIrderdicie een 7 to 14 Not less than 14 


It is customary to leave some shores in place under the bottoms 
of beams, girders, and slabs, for a week or two after the side and 
bottom forms have been removed. 

When the forms are removed, the units to be re-used showd be 
cleaned, repaired, and piled. The rough lumber should have old 
nails removed, surfaces cleaned, and be sorted and piled for future 
use. 

In general, the successful removal of the forms requires care, 
skill, and experience upon the part of the foreman. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 81 


Exercises.—What kinds of lumber should be used for forms? 

What size of nails should be used for nailing 1-in. stock on 2- X 4-in. 
joists? For nailing 2-in. planks on joists? 

What sizes of stock are used for forms for floor panels? Joists? Wall 
forms? 

With an average temperature of 65°F., how long should wall forms remain 
in place? Beam forms? 

What is the object of using double-headed nails? 


JOB 26. TYPES OF WOODEN FORMS FOR CONCRETE 


In this job, brief descriptions of the more general types of 
forms will be given. Forms for special work will be described 
in later jobs. 


Fic. 25.—Forms for a reinforced concrete building story. 


There are two types of wall forms, continuous and panel. 
Continuous forms are commonly used for basements walls. Such 
wall forms usually consist of 1-in. sheathing, nailed to 2- X 4-in. 
studs, and held in place by horizontal and diagonal framing. 
When the outside earth is hard and firm, it may be used as a part 
of the forms. Wire ties and wooden spreaders are frequently 
used in wall forms of this type. 


82 CONCRETE PRACTICE 


Panel or sectional forms are economical for high walls, or on 
jobs where the panels can be re-used. In forms of this type the 


ty TD ¢ 
Fig. 26.—Basement wall form. 


sheathing is nailed to vertical studs to form a panel and the 
panels are held in place by horizontal wales or rangers. Either 


Fia. 27.—Self supporting wall form. 


the studs or wales are double timbers spaced to permit the 
passage of the tie bolts between them. The wall panels may be 


_~PROPORTIONING, MIXING, AND PLACING CONCRETE 83 


bolted or tied together with wire. Spreaders of wood or iron pipe 
are used to keep the forms the correct distance apart. These 


R Sheeting or Forr? Boards 
SS 
AS G--Studs 


\ 


PANERA STL LPS LLL LLL IN LLL 


wy 
mp \ ft 


= “Spreader 


woo 


DP 
SA A 
Sid, 


y NY +. ‘OF 
f'h_fh) cea! Sm SC TE YE dy by 
MY/ fff e ccc io WZ 
NY e [a Pan ALTA aM i 
Vie ; ° sal, a 4 
u : —— fl 1S 


fac and tie rods in posrtion 


Fig. 29.—Ties for wall forms. 


spreaders are removed as the forms are filled. Sometimes the tie 
bolts pass through the pipe spreaders. In such cases, the spread- 


84 CONCRETE PRACTICE 


ers are left in the wall. Wooden washers should be placed at the 
ends of the pipe, so that the iron will not be exposed and later 


roy 
NN 
¥ yi bs 


lz 


Fic. 30.—Ties for wall forms. 


discolor the wall surface. When the concrete has hardened, the 
tie bolts (passing through the spreaders and washers) are easily 


| 
aah = = 
NE Za Za 
| ING: df 4 
UN 2 Sczerve eo eezeeceatg ez 
IN Z4 za 
HS ; Bolt removed offer 3 
WA mae Swe sé 
ra concrete 1s set ----~ g 
1 Jos Se rcoeate GILL, A 
ig Za PAE, a LAA 


Ise of wire form tightener 


One face of wall to be finished 


Fiq. 31.—Ties for wall forms. 


removed, the wooden washers cut out, and the holes filled with 
cement mortar. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 85 


QBIEL. 


Pe. WW fe SN — 


Fig. 33.—Column form. 


Fig. 32.— Column form. 


Fig. 34.—New England column clamp. 


86 CONCRETE PRACTICE 


Z "Angle fillet ia. coeners 


yf a - i 
pak r 8 lagging planed four sides: + 
3x4°Clip. f % ie 
. aE Roe TES 3 
§ ; LT. ar rT Tiel. 
S : | 1 + od alee 
b iN , g 
ext] i | 1 as 
ay y : 
Sen: Clip 
Original First..Reduction Second Reduction! 
Pieces “b” removed, Pieces 2” and ‘b” removed, 
side x" moved in, 34" side x" moved in, 314" cut 
clea cut down and /z2" down and Ix 2" nailed 
se? in as shown behind. behind cleats 
boarding. 


Fig. 35.—Method of reducing size of column forms. 


Fig. 36.—Gemco square column Fa. 37.—K. & W. square column clamp. 
clamp. 


Fic. Pr eir e a round column Fic. 39,— Universal round column 
clamp. clamp. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 87 


There are several varieties of patented wall ties on the market, 
most of which are devised so that parts or all of them may be 


Se ee ooo ooo eo eo ee 


rN 
[* 8] 


gH 4 


Hy 
b= 


eS “\x Ind. cate 
Ind, cates 
e 2s Centering post§ 
wader gts 


Fia. 40.—Flat slab floor forms for interior floor bay. Top view. 


me) j Panelo, 


at girt joint 2” 
ee below 


"9" 8" of AA" 
Frough Fosts.\ 


4-104 double, 


headed nails 


Cross Section 0G 


Lo9-8/CWwNoils 


Fiq. 41.—Flat slab floor forms for interior floor bay. «Side view. 


removed after the concrete has hardened. If iron ties are 
exposed in the wall surface, these ties may later cause a discolora- 
tion of the wall surface. 


88 CONCRETE PARCTICE 


Concrete building columns are usually square, rectangular, 
round, or octagonal in shape. Round columns usually have 


---*---Fanel Joists «+= == 


‘. I 
 'x6"Rough 
Graces 


9x4" or bx gl! 


Fig. 42.—Flat slab floor forms for interior floor bay. Side view. 


metal forms, while the forms for the others may be made of wood. 
Wooden column forms are usually made up of sections held 


TSX bas 


Fig. 43.—Forms for beam and girder floor system. 


together by yokes, which also act as cleats. Hach section is 
commonly used as a unit and forms one side of the column. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 89 


al 
puogd’. 


maa 


Xe #27? |]. I] IX 
(apg wosg|, { 


-- 
=== 


1 
oe 
wood woag: |x 


-Opig woag Hae an 


—_ ert I | | 
ie Sp 
xX) 


3 
' 
3 
‘ 
‘ 
t 
7 
t 


7 
) 
' 
' 
! 


=) 


; 5 


II, 
“ = 


a 
S 
S 
q 


pls ae 


§ Lop fO 4aPLD 


Fig. 44.—Plan of beam and girder floor formwork. 


a 


so OE a LL “Floor Poner 


i: Sian = t Wires — Se 
om 2 as 
| Leager' || 


Eee 
a ot Ledger i 
ber a as "XG "“ibband ema 


ih 
eet 1 


es J 


| eels 


Li SS 


Fig. 45.— Details of beam and girder floor formwork. 


90 CONCRETE PRACTICE 


A small opening is left at the bottom of each column form for 
the removal of sawdust, shavings, dirt, etc., just before the 
concrete is poured. ‘There are various types of yokes and clamps 
on the market for holding the section of a column form together. 

Ordinary floor forms for reinforced concrete buildings are 
of three types: flat slab, beam and girder, and slab. The flat- 
slab forms are very easy to construct unless there are drops 
around the column heads. These forms consist of sheathing 
supported by joists and stringers, which are in turn supported 
by posts or shores. 

The forms for beam and girder floors are more complicated in 
their arrangement and construction, and waste more lumber. 
Girder sides are usually continuous and have the beams framed 
into them. ‘The beam and girder sides, beam and girder bottoms, 


Bridging -:+~ 


“Galvanized Iron 
covering 


Fic. 46.— University of Wisconsin slab forms. 


and slab panels, are made up separately, and erected after the 
column forms are in place. 

The slab type of floor consists of panels in which the slab acts 
as both beam and slab, and which is supported by girders carried 
by columns. The forms for this type of floor are often of wood 
with a metal covering. These wooden boxes are supported by 
planks and shores. This type of floor form is economical when 
the building is rectangular in shape and the columns are uni- 
formly spaced. 


Exercises—Name the two types of wall forms. What is the difference 
between them? 

What are ties and spreaders? What are shores? What are column 
yokes? 

Name the three kinds of floor forms for reinforced concrete buildings. 
What are the essential differences between these types of floor forms? 
(Use sketches.) 


PROPORTIONING, MIXING, AND PLACING CONCRETE 91 


JOB 27. METAL FORMS 


Metal forms have been used for sewers, tunnels, tanks, and 
retaining walls, and are now coming into use for walls, columns, 
beams, and slabs, due partly to the increasing scarcity and cost 
of suitable form lumber. 


Fig. 47.—Blaw Knox Co. steel wall forms. 


Wall forms are generally made in panels, and are held together 
by the wires, or some special form of clamp. Three common 
types of steel wall forms are the Blaw (Blaw Knox Co.), Hydrau- 
lic Steeleraft (Hydraulic Steeleraft Co.), and the Metaforms 
(Metal Forms Corp.). 


92 CONCRETE PRACTICE 


The Blaw forms consist of metal standard panels reinforced 
on four sides with small angles. Special panels are provided 
to allow for various sizes and shapes of walls. The panels are 
fastened together by horizontal and vertical liners held in place 
by small wedges in slots. 


Fig. 48.—Metaforms steel wall forms. 


The Hydraulic Steelcraft forms consist of light, pressed steel, 
U-shaped vertical liners and horizontal ribs, supporting form 
plates backed with wood. ‘The framework of ribs and liners is 
erected first, the reinforcing steel is placed, and then the plates 
are fastened to the ribs and liners. Floor and roof slabs are 
constructed of the same equipment. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 93 


Metaforms consist of 2-ft. square sheets of annealed metal, 
reinforced on all four sides and in the middle with a 1 X 1-in. 
angle. The sheets are held together by clamps fastened to the 
side angles. These forms may be held apart by metal spreaders 


Fic. 49.—Blaw Knox Co. steel circular column forms. 


and tied by wire. Horizontal ribs and vertical liners are used 
to keep the units more rigidly in position. 

Practically all forms for round columns with flaring heads 
are made of metal, and several metal forms are on the market 
for square, rectangular, and octagonal columns. Adjustment 
in the height of the forms is obtained by telescoping the lower 


94 CONCRETE PRACTICE 


Plan of Forming of 24"Column 


Upper Unit 
Upper Unit : 
io rit Lowe//Unit 


Flan of Joint where Units 
Telescope 


7 Apron strip 
Top Digmeter- 
#2 Opening 


Columa Extensiop 
Unit 


Section of Head,One Head 
Extension and Column Extension 


Length of Shaft 


_-Apron Strip 
Top Diam 
#3 Opening: 


Unt 
Extension 
ait. 
Section of Head & 
Column Extension 


26" Plank. 
spaced 24"or 25%C foe. 


SSS 
La 


i Ss 
LAA 
\ 
< A 
———S—SS 
aS 


Z4"Column clarips eA 


Fig. 51.—G. F. steel tyle. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 95 


sections. Adjustment in diameter is provided for by use of 
form panels of different widths. 

Metal floor forms are of two types, removable and non-remov- 
able. ‘These forms are usually made of pressed steel, and come 


Fic. 52.—Steel floretyles. 


in standard widths. The lengths may be fixed, or may be made 
adjustable by telescoping one section on another. Some of 
the removable types of metal floor forms are the Meyer Steel 
Forms, Berley Floor Cores, and Wiscoforms. In the non-remoy- 


Fic. 53.—Steel floredomes. 


able types of steel floor forms, the steel forms take the place of 
hollow tile in the floor. Some of the types are G. F. Steel Tile, 
Steel Floretyles and Floredomes. The pressed steel is often 
ribbed or corrugated, to provide greater stiffness and rigidity. 
Metal floor forms usually come in depths of 6, 8, 10, 12, and 14 


96 CONCRETE PRACTICE 


in., and the width and length vary with different styles and differ- 
ent companies. Removable forms are usually well oiled before 
the concrete is formed, while non-removable forms are not. 

Special metal forms are used for the construction of sewers, 
tunnels, etc. 


ic a Standard Panel 


—26 
~ \ Section thru Depressed Fane) 
Fig. 54.—Metal panel forms for flat slab floor. 


Exercises.—Describe one type of metal wall form. 
Why are metal forms used more often than wooden forms, for round 
columns with flaring heads? 


JOB 28. REMOVAL OF FORM MARKS AND MECHANICAL SURFACE 
FINISHING 


In general, the treatment of the exposed concrete surface 
depends upon the results that are desired. In many buildings 
and bridges, not only are the form marks removed, but the sur- 
face is finished so as to improve the architectural appearance of 
the structure. In case of the floors, it is sometimes desirable to 
improve their wearing qualities. | 

The form marks can be reduced considerably by constructing 
the forms so that their inner surfaces are true, smooth, and tight, 
and then spading the concrete when it is placed in the forms, so 
that air pockets are eliminated, the coarse aggregate is forced 
away from the forms, and a thin layer of compact mortar is 
next to the form surface. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 97 


Common form marks are fins, edges, blemishes, and wood 
graining. Fins may be easily removed with a hammer and 
chisel. Edges may be removed by the same means, but require 
more and careful labor. Blemishes and wood graining may be 


Fia. 55.—Fine textured concrete Fic. 56—Machine made con- 
surface obtained by cutting. crete block with coarse limestone, 
no facing mixture, and very little 

sand and cement. 


ground off, or may be concealed by brushing with a thin, neat, 
cement grout. Holes caused by bolts, washers, wires, etc., may 
be filled with a mortar of the same proportions as that used in 
the concrete. When portions of the surface are honeycombed, 


Fie. 57.—A cut concrete stone Fie. 58.—Tooled surface of con- 
surface. crete trim stone. 


about the best method of treatment is to cut out the honeycomb 
and replace it with good concrete. 

The more common methods of mechanical surface finishing 
are washing, acid treatment, brushing or scrubbing, rubbing, 
tooling, sand blasting, and sand float. 


98 CONCRETE PRACTICE 


In the washing treatment, the outer film of cement and sand 
is removed by use of a stream of water before the concrete has set. 
This treatment is rarely used, because of the danger of leaving 


Fig. 59.—Special surface finish. Concrete rubbed and polished. 


the green concrete unsupported before it has set. Washing 
should be done in from 6 to 8 hrs. after the concrete has been 
poured. 


-PROPORTIONING, MIXING, AND PLACING CONCRETE 99 


Scrubbing or brushing consists of brushing the surface of the 
concrete as soon as the concrete has set enough to hold the par- 
ticles in place. An ordinary stiff wire or bristle brush used with 
a firm, even pressure gives uniform results. Water should be 
used, when brushing, to wash off the surface. The time required 
for hardening before brushing varies from about 24 hrs. in sum- 
mer to several days in cold weather. If the coarse aggregate is to 
be exposed, then it should be spaded towards the form surface 
when the concrete is poured. 

Acid washes are often used in connection with brushing to 
improve the appearance of the surface. The acid tends to eat 
away the cement from the surface of the sand and stone and, 
consequently, the treated surface must: be thoroughly washed to 
remove all traces of the acid. The acid solution is made by mix- 
ing 1 part of hydrochloric (muriatic) acid with from 4 to 8 parts 
of water. A 1:8 solution is strong enough for very green con- 
crete, while a 1:4 solution, together with vigorous brushing, may 
be required after the concrete has hardened. 

Rubbing the wetted concrete surface, as soon as the forms are 
removed, with a fine-textured brick, soft stone, carborundum, 
emory, or other abrasive material will give a smooth surface of 
uniform appearance. If a rubbed surface is planned, the coarse 
ageregate should be well spaded back in the forms, when the 
concrete is poured. For best results, the forms should be 
removed in 1 or 2 days (in warm weather). 

After the concrete has been thoroughly hardened, it can be 
tooled, hammered, crandaled, or ground, until a surface of uni- 
form appearance is obtained. The coarse aggregate should be 
spaded back when the concrete is placed in the forms. Tooling 
permits of a variety of pleasing surface finishes, and need not be 
done until the concrete is 2 weeks old or older. 

Sand blasting gives a pleasing appearance, but this method is 
not economical unless there is a large amount of comparatively 
unbroken areas to be treated. The concrete should be thor- 
oughly hardened (at least 1 month old or more). All air pockets 
or depressions should be first repaired, and all fins, edges, and 
blemishes removed by tooling, as the sand blast affects the surface 
uniformly. Corners and angles must be protected if their sharp 
outlines are to be kept. A 14-in. nozzle, a nozzle pressure of 


100 CONCRETE PRACTICE 


from 50 to 80 lb., and a clean, sharp, dry silica sand passing a 
No. 8 sieve will usually give good results. ~ 

In the sand-float method of finishing, the forms must be 
removed before the concrete has fully hardened, and the surface 
must be rubbed with a wooden float with a uniform circular 
motion. Fine sand should be added and rubbed into the con- 
crete surface until the surface has a uniform texture and 
appearance. 


Exercises.—State the five classes of surface finishes. 

How may form marks be removed? 

Name five methods of mechanical surface finishing. 

Describe the acid wash method. 

Describe one form of surface finish by tooling (brush, hammering, crandal- 
ing, etc.). 


JOB 29. USE OF COLORED AGGREGATES AND PIGMENTS 


A very pleasing and satisfactory surface appearance may. be 
obtained by the use of colored aggregates in the concrete mix. 
The successful production of the surface depends on the correct 
grading, proportions, mixing, placing of the concrete, and upon 
the method of finishing the surface. When these aggregates are 
expensive, they are used in a facing mixture, which is usually 1 
or 114 in. thick. A good method is to divide the form with iron 
plates, and pour the facing and backing together, gradually 
raising the plates as the molds or forms are filled. The propor- 
tions of the facing mix commonly used are 1 part of cement to 
114 parts of sand to 3 parts of pebbles or screenings by volume. 
Portland cement (common or white), white sand, marble chips, 
granite screenings, mica, slag, feldspar, and garnet sand are some- 
times used. When the mix has hardened sufficiently, the surface 
is brushed or sprayed with water to remove the surface cement 
and expose the aggregates. An acid wash may be used when the 
acid will not affect the color and luster of the special aggregates. 

Mineral colors or pigments (up to 6 per cent by weight of the 
cement and carefully mixed dry with the cement) may be used to 
give color surfaces. If there is much danger of the pigments 
reducing the strength of the cement, the colored mix should be 
applied as a veneer, as described in the previous paragraph. 
The yellows, browns, reds, and blacks produced by iron oxides 


-PROPORTIONING, MIXING, AND PLACING CONCRETE 101 


give permanent color, while the blues and greens may fade. 
Chromium oxide will give a permanent green. The correct 
amount of coloring matter to be added will depend partially upon 
the aggregates used, and may be found by experimentation. The 
following table, from Sabin’s ‘“‘Cement and Concrete,” gives an 
idea of the amount of coloring matter required: 


Cotorinc Marrer RequirED BaAsEep on A 1:2 Mortar 


Color produced by 


peel Wayeneriide so euib. per 100 Ib. 
lb. of cement of cement 

Lary si ly OO a Light slate Dark-blue slate 
PURSUE) ek Light-green slate Bright-blue slate 
MOR ERA P COU NTC APE By cass |e dw se ced ee ve ew als Bright-blue slate 
CLS "OTs chee ee Light green Light buff 
TStIETV LACES, cee a. pes es ss Light pinkish slate | Chocolate 
Sen Tes Slate, pink tinge Dull pink 
igi (a Pinkish slate Light brick red 


Concrete surfaces may be painted by a number of good paints, 
which have been placed on the market for that purpose. The 
surface should first be primed with a solution of magnesium zinc 
fluosilicate or zinc sulphate in water, or with a commercial floor 
hardener, to aid in keeping the paint from peeling off. 


Exercises—What colors would be given to a concrete surface by using 
mica as a fine aggregate? Slag? Feldspar? Garnet sand? 
How many a veneered surface be applied to a concrete block? 


JOB 30. PREPARATION. OF WEARING SURFACES 


Wearing surfaces, such as concrete floors, require a special 
preparation and treatment, if they are to be satisfactory, and 
wear and dust reduced to a minimum. In general, the mix of 
which the average concrete floor is made will not give a good 
wearing surface, because of too lean a mix, too wet a mix, too much 
or too little tamping, excessive troweling, use of aggregates 
having a low abrasive resistance, and presence of laitance. 


102 CONCRETE PRACTICE 


An old concrete floor which is not satisfactory in regard to wear 
and dust may be improved by one of three ways: (1) grinding 
the surface to remove laitance and loose material from the surface; 
(2) painting with special paints; and (3) roughing the old surface 
and applying a wearing coat at least 1 in. thick. In the third 
method, the old surface is roughened, cleaned, washed, and 
thoroughly wetted, and then a neat cement grout is applied, 
followed by a wearing course mix before the cement grout has 
attained initial set. 

A new concrete floor can be satisfactorily made in regard to 
wear and dust, if the aggregates used have a high abrasive resist- 
ance, and have been screened and washed. The mixshould not be 
leaner than 1 part of portland cement to 214 parts of aggregate, 
and the least amount of mixing water that will produce a dense 
mix should be used. ‘The materials should be mixed thoroughly, 
carefully placed and tamped (but not too much), the surface 
screeded even, and finished with a wood float without excessive 
troweling. Any excess water should be immediately drained or 
otherwise removed. The surface should be kept wet for at least 
10 days in the case of floors, and then ground Ue a surface- 
grinding machine. 

It is usually more satisfactory to construct the floors in two 
courses, base and wearing. The base course is laid ya in any 
concrete work, and the wearing course added within 14 hr. after 
the base course is placed. The wearing course must << at least 
1 in. thick, and of a mix not leaner than 1:2!4 by volume. 
Screened and washed aggregates having a high abrasive resist- 
ance should be used. The floor surface should be kept wet for 
at least 10 days after placing, and then ground with a surface- 
grinding machine. 

‘“‘Granolithic finish” is a term frequently applied to a concrete 
wearing surface which contains crushed granite or other hard 
stones as an aggregate, and which has been usually ground by 
means of a grinding machine. 

Terrazzo finish may be made by either one of two methods. 
One method is to use a mix of 1 part of portland cement and 214 
parts of crushed marble (or other stone as specified), and enough 
water to produce a dense concrete. This concrete is spread on 
the base course, and worked down to a thickness of not less than 


PROPORTIONING, MIXING, AND PLACING CONCRETE 108 


1 in. by patting or rolling and troweling. The marble should 
pass a /4-in. screen, and be clean and free from dust. After being 
kept wet for 10 days, the surface may be ground to a plane sur- 
face with a surface-grinding machine. When finished, the 
surface should show about 95 per cent of hard aggregates and 5 
per cent of cement. 

The other method of making a terrazzo finish is to mix 1 
part of portland cement and 2 parts of sand and enough water 


Fic. 60.—Close up photograph of terrazo wearing surface. 


to produce a plastic mortar, which is spread on the base course 
to a depth of not less than lin. Clean, dust-free, crushed marble 
passing a }4-in. screen is then sprinkled over the fresh mortar 
surface and pressed or rolled in. After the surface has been 
kept wet for at least 10 days; it is finished with a surfacing 
machine. 

A terrazzo finish may be applied to an old concrete floor pre- 
pared as described above. 

Many pleasing effects can be obtained by using colored aggre- 
gates, such as red granite chips, feldspar, and colored marbles 


104 CONCRETE PRACTICE 


and pigments. In many instances, tile patterns have been 
inlaid in concrete floors with satisfactory results. 

Painting is satisfactory, when the wear is not great. The 
paint may be prevented from peeling by using a priming coat of 
zine sulphate solution (8 lb. of zinc sulphate to a gallon of water). 
Oiling floors has sometimes been successful in preventing dust 
when the traffic is light. 


Exercises.—What is a granolithic finish? 

What is a terrazzo finish? 

Describe one method of making a terrazzo finish. 

Why should the wearing surface be 1 in. thick or more? 

What is the object of grinding a floor? 

What kind of aggregates tend to make a good wearing surface? 


JOB 31. CONCRETE BUILDING UNITS 


The concrete products industry has grown slowly and surely, 
and is now a substantial part of the whole concrete industry. | 


K 
Fic. 61.—Horizontal cross sections of representative types of concrete block. 


Many of the early blocks made were failures, due to poor 
machines, wrong materials, incorrect proportions and consisten- 
cies, lack of skill in molding, improper curing, and wrong shapes 
and sizes. In the last few years, the concrete block industry 
has progressed, due to the increase in skill and experience 
‘of the workers, and the aid of the cement and machinery 
manufacturers. 

There are two main divisions in the concrete products industry : 
(1) the production of standard building units in quantity; and 
(2) the manufacture of trim stone, blocks, and brick with special 
ornamental facings, and specially molded ornamental work. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 105 


The concrete blocks are of various sizes and arrangements of 
_walls and cores, though practically all of them provide for hollow 
air spaces. The front and rear walls of the block may be tied 
together with concrete or metal ribs, the use of metal preventing 
the passage of water through the block. In some instances, 
the blocks are designed so that the wall thickness is made up of 
two or more blocks, so as to give a discontinuity of concrete 
through the wall. Figure 61 shows the cross-sections of various 
types of concrete blocks. The dimensions of the standard blocks 
vary, ee from 734 to 12 in. thick, from 8 to 12 in. high, and 
from 1534 to 32 in. long. The 734- X 8- X 1534-in. size is the 
most common. 

Concrete building tile vary from about 5 in. high X 3 in. wide, 
and 12 in. long to 12 in. high, 12 in. wide, and 32 in. long. 
Concrete brick are made in various sizes, the most common being 
214 in. high, 334 in. wide, and 8 in. long. 

The Bureau of Standards recommends the following sizes of 
concrete building units: 


CONCRETE BLOCK 


Height, Tolerance,| Width, | Tolerance,| Length, | Tolerance, 
inches inches inches inches inches inches 
734 minus 1g 6 minus 14 1534 minus 1g 
734 minus 1¢ 8 minus 14 1534 minus 1g 
734 minus 1g 10 minus 14 1534 minus 1g 
134 minus 1g 12 minus 14 1534 minus 1g 
CONCRETE BRICK 
; Height, Width, Length, 
Kind ; ; é 
inches inches inches 


Paceland commion............+. 214 334 8 


106 CONCRETE PRACTICE 


CONCRETE BuILDING TILE 


Kind Height, Width, Length, 
| inches inches inches 

Load, beating... 4. cou eee ae 5 334 12 
5 8 12 
5 12 12 
Partition. 32%); so tae eee eee 3 12 12 
f 12 12 
6 12 12 
8 12 12 
10 12 12 
12 12 12 


A plus or minus tolerance of 3 per cent is permissible in each of the three 
dimensions of concrete building tile. 


The materials used, in: the manufacture of concrete building 
units, are portland cement, and fine and coarse aggregates. In 
general, materials suitable for first-class concrete work are also 
suitable for making concrete building units, except that the 
maximum size of the aggregate rarely exceeds about 14 in. and 
should always be less than half of the smallest dimension of the 
block, brick, or tile. For special surfaces and finishes, various 
kinds and types of aggregates are used like those mentioned in 
previous jobs describing ornamental finishing of concrete surfaces. 

The proportions used for the mixes vary from about 1:3:4 to 
1:1:114 by volume, depending on the qualities of the aggregates 
and the specifications to be met. Some of the larger manufac- 
turers are now proportioning their mixes according to the latest 
scientific methods. 

The mixing may be done either by machine or by hand. Ma- 
chine mixing is preferred. 

The molding may be done by hand or machin, except that a 
machine is required in the pressure process. Concrete standard 
building units are usually machine molded, while concrete stone 
trim are hand molded. At present, there are various molding 
machines on the market. The construction of the machines 
varies with the consistency of the mix, the method of compacting 
the concrete, and the ideas of the manufacturer, 


PROPORTIONING, MIXING, AND PLACING CONCRETE 107 


The following three methods are commonly used in the 
manufacture of standard concrete building units: 


Fig. 62.—Hand tamp concrete block machine. 


1. Dry Tamp Process——The materials are mixed to a damp 
consistency, and are then tamped in the molds by hand or 
machine tampers. Care should be taken not to get a consistency 


Fig. 63.—Pressure concrete block machine. 


. 


which is too dry. This method is frequently used to make con- 
crete stone of special shape or surface finish, because the molds 
may be of any desired shape and size. 


108 CONCRETE PRACTICE 


2. Pressure Process.—A somewhat wetter consistency is used 
than in the dry tamp process. The mixed concrete is placed 
in the molds and compacted by pressure, applied either by 
mechanical levers or a hydraulic piston. 

3. Wet Cast Process——In this process, the consistency should 
be such that the concrete will flow readily. The mix is poured in 
the molds, and puddled or rodded to remove the air and to get 
the larger particles away from the sides of the molds. No 
tamping or mechanical pressure is used. Frequently, the con- 
sistency is made too wet for the best strength results. 


Fic. 64.—Metal gang molds mounted on car. 


In the first two processes, the concrete is so dry that the molds 
can be removed at once from the blocks, while in the last method 
the molds cannot be removed until the concrete has attained hard 
set. In all three processes, care should be taken to secure density 
and uniformity of the concrete. 

In curing, care should be taken to prevent the too rapid drying 
out of blocks. After the molds are removed, the blocks and 
brick should be protected from wind currents, sunlight, dry heat, 
and freezing for at least a week. During this time, the blocks 
should be thoroughly sprinkled at least once a day. After the 
first week the blocks should be sprinkled, or otherwise moistened 
occasionally, until they are used. When cured by any natural 


PROPORTIONING, MIXING, AND PLACING CONCRETE 109 


Fia. 65.—Concrete products factory. (Block department in background.) 


R = Curing rooms. 

S = Second floor (or intermediate floor above curing rooms) where a battery 
of five mixers are located. 

E = Elevator for boxes of mixed facing material. 

B = Bucket (a part of an electric monorail system) for delivering mixed 
concrete to machines and at bankers. 

H = Hoppers to receive mixed concrete. 

C = Block car. 


Fia. 66.—Part of concrete block department of a concrete products factory. 
Block machines with hoppers above are shown in the background and block 
cars in the foreground. Note the two floor levels. The cars run on tracks into 
pits so that four decks can be loaded without too high a reach. The empty 
‘‘decks’’ from the car at the left are placed on the car at the right as it is piled. 


110 CONCRETE PRACTICE 


process, concrete building units preferably should not be used 
until they are 28 days old. 

The curing of concrete building units may be hastened by 
placing them for at least 48 hr., when they are removed from the 
molds, in an atmosphere of moist steam. The temperature of 
the curing room should preferably be from 100 to 180°F. The 
saturated steam provides heat and moisture, and accelerates the 
hardening of the concrete. After removal from the steam-curing 
room, the building units should be stored for a week before using. 

Concrete building block and tile should pass the American 
Concrete Institute Standard Specifications for Concrete Building 
Block and Building Tile (Serial Designation P-1A-25) given 
in Appendix 11. It should be noted that these concrete building 
blocks and tile are divided into heavy-load-bearing, medium- 
load-bearing, and non-load-bearing units, according to their unit 
compressive strength. Concrete building blocks and tile that 
are not to be exposed to the soil and weather are not required to 
pass the absorption test. The average unit cross-bending strength 
(modulus of rupture) of concrete building blocks, tile, and brick 
will be about 10 per cent of the average unit compressive strength. 

Concrete building brick should pass the American Concrete 
Institute Standard Specifications for Concrete Brick (Serial 
Designation P-1B-25) given in Appendix 12. 

Concrete building units are being used at an increasing rate in 
all parts of the country. Some of the more common uses are 
basement walls, walls for stores, residences, barns, silos, etc., 
partitions, and in most any place when a light, durable, fireproof 
wall or partition is desired. 

Exercises—What are the differences between concrete building block, 
tile, and brick? 

What are the compressive strength requirements of concrete building 
block and tile? Of concrete building brick? 

What are the absorption requirements of concrete building block and tile? 
Of concrete building brick? 

A compressive test on concrete building block gave the following results: 
1215, 1017, 835, 727, and 971 Ib. per sq. in. In what class do these blocks 
belong? 


JOB 32. CONCRETE TRIM AND ORNAMENTAL STONE 


There are special machines on the market for molding different 
special concrete units, as well as a large number of special molds 


PROPORTIONING, MIXING, AND PLACING CONCRETE 111 


for sills, lintels, balusters, belt courses, cornices, and other trim 
stone, and various architectural pieces. In addition to these 
special machines, it is necessary for the concrete products manu- 
facturer to have skilled workmen to 
make intricate designs of concrete 
stone to meet the demands of the 
architects. 

Most of the molds for concrete 
dimension stone (sills, lintels, belt 
courses, cornices, etc.) are constructed Aye Bees Ma tdne plagter mold. 
of wood, preferably white pine. For ing. 
simple work, the mold consists of side 
planks and end pieces resting on a pallet, and held together by 
clamps. In dry cast work, the facing mixture, if one is used, is 
placed in the bottom of the mold, up to the front, and part-way up 
the ends, as desired, and then the backing mixture is added and 


Fig. 68.—Plaster molds. The dark modeled part is the plaster model. The 
parts A and B are the first two pieces of a plaster mold. 


tamped in place. The concrete is struck off smooth at the top, a 
layer of bedding sand added, and a plank placed on top of the sand 
and clamped in place. ‘The entire mold and contents are turned 
over, so that the concrete stone is right-side up when the mold is 
removed. When the concrete has hardened sufficiently, the mold 
pieces are removed, and the concrete stone left right-side up on 


112 CONCRETE PRACTICE 


the plank. A very dry consistency is used, as the molds are 
removed after a short time. 

In the wet cast method, a smooth concrete floor or table top is 
shellacked and oiled, and the form pieces erected thereon, with 
the necessary insert pieces and partitions. A concrete of rather 
wet (quaky) consistency is used, and the concrete stone left in 
the molds until it has thoroughly hardened. 

Various metal molds are now made for different ornamental 
pieces and standard architectural units. ‘These molds need only 
to be cleaned and oiled, and can be used many times. 

When necessary, the individual stones (such as lintels) may 
be reinforced against bending. 


Arch stone — Two or three piece pattern 
depending on direction oF draw” \ 


Nails removed before 


shown by arrow A" wood 
op pattern Us completely ® 
moulde 7 


Note '- Incasé patterrr. 

4s drawn from sand as 

box is not required and 

1 pattern split in three 

parts as shown . 

mi) Sy solid /ines ‘ae 

|| Note:- In case pattern fs drawn as shown_. 
7 arrow ‘B" if is split as shown by 

‘ih. dotted lines and wood Lor is used 

Ay 70 take care of check 


Fig. 69.—Splitting pattern for Fia. 70.—Two ways of splitting a pattern. 
making sand mold. 


Plaster is used quite extensively for making models and molds 
for ornamental concrete stone. Skilled workmen can make a 
suitable plaster mold from the architect’s drawings. When the 
plaster model is finished, it is shellacked and oiled, and a mold 
made over the model. ‘The model is removed from the mold, 
and the mold surface shellacked and oiled before the concrete 
is added. With plaster molds, the concrete mix is quite dry, and 
is lightly but firmly tamped in the mold. Draw molds may 
be used when there is no undercut, and when the undercut sec- 
tions of the mold are made so that they will readily separate 
from the main part, and can be removed easily after the main 
part of the mold had been drawn. Drawn molds must be smooth 
and true, and tapered a little, so that they can be withdrawn 
without injuring the concrete. Plaster molds may be used several 
times. 


PROPORTIONING, MIXING, AND PLACING CONCRETE 113 


Gelatin or glue molds should be used where there is much 
undercut, which would necessitate making the plaster mold in 
many pieces. In making a glue mold, the model mold is first 
covered with paper, and a thin layer of modeling clay added. 
This clay covering is greased, and plaster added over it, to form 
a Shell with several holes and air vents. When the plaster mold 
is hard, it is removed, and the clay and paper cleaned from the 
model. The surfaces of the model and mold are shellacked and 
oiled, the model is placed in the mold, and the space between 
them filled with hot glue. The air vents can be stopped with 
clay as the space is filled. When the glue is hard (requiring 
about 24 hr.), the plaster mold is first removed, and then the 
glue mold is cut into a few parts and removed from the model. 
The consistency of the concrete used with a glue mold is wetter 
than that used with a plaster mold, because concrete cannot be 
tamped in a glue mold. A glue mold may be used about four 
times, after which the glue may be remelted and used for another 
mold. 

Sometimes various combinations of molds are used, such as 
wood strips in plaster molds, plaster inserts in wood molds, and 
small glue molds in connection with plaster molds. For difficult 
ornamental work, when much duplication is necessary, a glue 
mold is first made, then a glue model, and then several plaster 
molds from the glue model. When the work is intricate with 
much undercut, the plaster mold is cut away from the concrete 
and ‘‘ wasted,” no attempt being made to save the plaster mold 
for re-use. 

Sand molds are made by packing sand around models in core 
boxes, in about the same manner that molds are made for iron 
castings. The sand should be a fine sand which will mold well. 
The sand is wet to make it slightly damp, and it is often mixed 
with fine loam or plaster, and sometimes with an integral water- 
proofing powder. After the molding sand has been packed 
around the models, the models are removed or withdrawn, and 
the mold filled with concrete of a flowable consistency. Excess 
water should be avoided whenever possible. The sharp edges 
in the mold may be built up of wood inserts, as the sand edges 
may crumble. Draw molds may be used in connection with sand 
beds, if care is taken in the design of the draw mold, to taper it 


114 CONCRETE PRACTICE 


and provide removable inserts, when there is undercut. As the 
sand tends to stick to the concrete surfaces, it is nearly always 
necessary to give the concrete stone some surface treatment. 

Although most concrete block and dimension stone are made of 
the same mix and material throughout, it is very easy to provide 
facing mixtures, especially in the dry tamp method. Previous 
jobs describe various methods of making and surface finishing 
to secure different ornamental surfaces, which methods may be 
used in connection with concrete ornamental and trim stone. 
Colored effects may be produced by the use of good mineral pig- 
ments, as previously described. 


Exercises—Name the various methods of molding concrete trim and 
ornamental stone. ' 
Described, with a sketch, the making of a simple wood mold for a con- 
crete lintel. 


SECTION III 
CONTRACTS, SPECIFICATIONS, AND PLANS 


JOB 33. CONTRACTS 


A contract is an agreement, usually based upon a considera- 
tion, to do or not to do some particular thing which the law will 
enforce. 

A contract for construction work should be in writing. <A 
complete contract will include the following documents: adver- 
tisement or notice to contractors; information for bidders; form 
of proposal; general contract; bond; general specifications; 
detailed specifications; and plans and drawings. 

On some jobs, part of these documents may be omitted. For 
example, if one man contracts with another to build a house, 
perhaps only the general contract, general and detailed specifica- 
tions and plans would be needed. 

A general contract should include the following: introduction 
of agreement and date; name, description, and residence of par- 
ties; statement of agreement; list of documents included in con- 
tract; time of beginning and completion; payments—time and 
amounts; liquidated damages; provision for bond; and final 
clauses, date, signatures and seals of parties, signatures of wit- 
nesses, and acknowledgment. 

There are several kinds of construction contracts, such as 
lump sum, unit price, cost plus percentage, cost plus fixed or 
varying fee contracts. A lump sum contract is one in which 
the contractor agrees to do the work for a certain definite sum. 
In a unit price contract, as in excavation, the contractor agrees 
to remove the earth for a certain price per cubic yard. ‘The cost 
plus percentage contract is one in which the contractor receives 
the cost of the work plus a percentage of the cost for profit. 
Another form of contract is the cost of the work plus a fixed fee 
or profit, so that the amount of the contractor’s profit is the 
same regardless of variation in cost. Perhaps a more satisfac- 
115 


116 CONCRETE PRACTICE 


tory form is one in which the contractor receives the cost plus 
a fee or profit, which profit will be decreased if the cost is 
more than an agreed sum or vice versa. 


JOB 34. STANDARD BRIDGE CONTRACT 


The Wisconsin Highway Commission’s Standard Bridge Con- 
tract will usually include the following: (1) advertisement and 
notice to contractors; (2) proposal for bridge work including 
instructions to bidders and proposal; (8) contract; (4) bond; (5) 
specifications including general and detailed specifications; and 
(6) plans. 

In this job, the standard form of instructions to bidders, pro- 
posal, contract, and bond follow in order. Sample standard 
specifications and plans are given in following jobs. 

The advertisement usually does not conform to any standard 
form, but is written for each individual job and published as 
required by the laws of the state in which the job is located. An 
advertisement should contain the following information, though 
some of the items are sometimes included in the instructions to 
bidders: 

. When, where, and by whom bids will be received. 

. Location of work. 

. Amount and nature of work or mnt to be furnished. 

. Time of beginning and time of completion of work. 

Where plans and specifications may be seen or obtained. 
Where, and from whom, general information may be 
ained. 

. What security will be required with the proposal. 

. What security or bond will be required with the contract. 

9. When and where bids will be opened. 

10. When and where contract will be awarded. 

11. Reservation of right to reject any or all bids. 

12. Official signatures of officials receiving bids or letting 
contract. 

In all public work, the laws require that certain formalities 
be observed when advertising the work, receiving bids, and 
letting the contract. The contractor should note if all of the 
legal requirements have been met. 


Oor WN 


ob 


saad 


CoON 


CONTRACTS, SPECIFICATIONS, AND PLANS LEZ 


In private work, many of the formalities required in public 
work may be (and usually are) dispensed with. The advertise- 
ment may be omitted, the number of bidders may be restricted, © 
the wording of the contract may be changed to suit the individ- 
uals concerned, the bond may not be required, etc. 


PROPOSAL FOR BRIDGE WORK 


INSTRUCTIONS TO BIDDERS 


Proposals may be made on reverse side of this form or on other convenient 
form, but must refer to, and be in accordance with, the plans and specifica- 
tions on file, otherwise, they may be rejected as irregular. Only sealed bids 
will be considered. The right is reserved to reject any or all proposals and 
to accept any bid which may be most advantageous to the party of the 
first part. 

Proposals should be addressed to the Board of Supervisors of the Town, 
Village Board of the Village, or County Highway Committee of the County 
named as party of the first part in the contract, and be accompanied by a 
certified check for a sum equal to at least 5 per cent of the bid as a guarantee 
that the successful bidder will enter into a contract with the party of the 
first part, and will give a good and sufficient bond in a penal sum equal to 
the amount of the contract for the faithful performance of the work. Said 
guarantee shall be made payable to the Treasurer of the said Town, Village, 
or County. This guarantee will be returned to the bidder, unless, in case 
of the acceptance of his proposal, he shall refuse to execute a contract and 
file a bond as required in the specifications, within fifteen days of the accept- 
ance of the proposal, in which case the guarantee is to be considered payment 
for damage due to delay and other cause suffered from refusal or neglect to 
execute a contract, and shall become the property of the said Town, Village 
or County. 

Unless special instructions are issued specifying otherwise, all bids shall 
be a lump sum proposal for bridge complete, including superstructure and 
substructure. When superstructure and substructure are required to be 
itemized, the right is reserved to accept any bid for superstructure, and to 
use this in connection with any bid for the substructure alone. No award of 
substructure alone will be made on any itemized bid, unless bidder specifies 
that such award will be acceptable. All proposals made on bidder’s forms 
should state a specific sum of each of the items A, B, C, D, and E, but any 
repetition beyond specifying the item by letter and the sum bid therefor, is 
unnecessary. 

The plans and specifications are designed to be correct and consistent. 
Bidders must, however, examine, not only the plans and specifications but 
the bridge site as well, thoroughly and carefully, and submit bids on their 
own responsibility. Any estimate of quantities, which may be given either 
on the plans or otherwise, is believed to be accurate but its accuracy is not 
guaranteed and bids must be made on bidder’s own estimates. 


118 CONCRETE PRACTICE 


PROPOSAL 
TO CHES wis oon s wile de wie sae oielwigs estes ip Caumdilel vane 1 [pa ‘salto Cola p 10,lellore einer ele ote Ran ne ae et tae 
Gentlemen: 
The undersigned proposes to do the bridge work on the..................cceeeceeees 
Bridge iansthevces eniaeta a ee e Ones cock veld dee ca aes IO ee County, for 


and in consideration of the sums hereinafter specified. 


Item A 

Complete so: aie see teeta, Sess ee oe ae tie ey eee consisting of) cc 2 eee a oe dee 
for the sum Ol oes Fo lshe sores os sie be oem ope Seer Chuan eee Re ee Dollarsi(Sey- 7 eee ) 

Item B 

Any additional concrete masonry in the substructure of the same classification as on plans 
at no greater depth than shown on plans, if ordered; for, ..2 a2. see 
Dollarsi(SAco.e veces ) for each cubic yard in excess of the quantity shown on the plans. 

Item C 

Any additional concrete masonry in the substructure of the same classification as on the 
plans at depth greater than shown on plans, if ordered, for.................++ee+eeecee- 
Dollars ($f. sane case ) for each cubic yard in excess of the quantity shown on the plans. 

Item D 

If the quantity of concrete masonry required in substructure is ordered reduced, the 
undersigned hereby consents toa reduction Of... , 24 +s see ene eee Dollars 
(Sh. onan eve ) from the contract price for each cubic yard the quantity shown on plans is 


so reduced. 


Item E 

Any additional piling not shown on plans, if ordered, for...............scesceees cents 
(keene et. ee erg c), for each linear foot delivered on the work, plus.................-.e. cents 
(Era c) for driving for each linear foot for actual penetration. 


The above prices include furnishing the bridge work complete in place, including all 
materials, tools, machinery, labor, necessary forms and falsework, steel reinforcement and 
piling where shown on plans, doing all excavation, removing the existing structure or struc- 
ture replaced, and any other work which may be necessary in order to do the work included 
in each item for which price is specified, in full conformity with the plans and specifications 
and the requirements of the Engineer. 

The undersigned declares that he has examined the bridge site, the plans the specifications 
for the work for which this proposal is made, to his full satisfaction, and that if proposal is 
accepted he will execute a contract and file bond as provided in the specifications. 


eee eee eee eee ee eee eee eee ese eeeee 


CONTRACTS, SPECIFICATIONS, AND PLANS 119 


CONTRACT 


This Agreement, entered into this........day of............ , 192.., by and between 
<n eRe es County, Wisconsin, represented by its County Highway Committee, party of 
the first part, and 


(OH als Ge owla Golemt ot conbeg t Cre nner , party of the second part. 


WITNESSETH, That for and in consideration of the payments to be made by said party 
of the first part, hereinafter called the County, to said party of the second part, hereinafter 
called the Contractor, said Contractor hereby agrees to do, at his own proper cost and 
expense, all the Highway Bridge Work on that portion of the County System of Prospective 
nods ae) TEL ELOSRRERPAS) TEN ELODIE | 52s by Bey ee oD ACRE sR RO ee of 


aisle 0 Soca Ol Qeny Cae , in said County, which is shown on plans and speci- 
fications annexed hereto, and made part hereof, in full conformity therewith. Thesaid Con- 
tractor agrees further to begin work on or before.................-. , 192.., to complete 
BaAme not later than. <........5.. Loss ands voekeep the roads oar ee ee ee to travel 
during construction. 


Susi sete esiistiéi ele ni wis) eels) isi .8 (66) fu 5) oss 9 © 9 © © 6 6 616) 6 6 6 6 6 8 8 © 8) v6 80 4:0 © 8 © 6 6 eee 8 6 8 6 ee 8 ere 6 Oe 8 8 8 we 8 8s Oe 


And said County, in consideration of the full and complete performance of said Highway 
Bridge Work by said Contractor, hereby agrees to pay, in the manner provided in the speci- 
fications, to said Contractor, the sums specified in the proposal submitted by said Con- 
tractor, which proposal is hereto annexed and made part hereof. 

The Contractor shall pay all claims for the performance of any work or labor of the fur- 
nishing of any materials when the same pertains or is for or in or about or under this contract 
as required by Section 289.16 Statutes of Wisconsin, and shall have paid and discharged all 
liabilities for injuries which have been incurred in the said construction, under the operation 
of. sections 102.01 to 102.34 of the Statutes of Wisconsin, inclusive, and all acts amendatory 
thereto. 


Risatniie aisieseeaiel= ial eue «Sle sb > alse) © 6b 6 6 és ¢ © 6 © ©) 0's 0 6 wie & 6 6 9 0 6.0 0 es Sw fe os eee Oe he me 8 wh ete 6 ae 6 


[Miter stata ate eis Sitaels & ela 6s se « fo 6s 16 6-0 6 © 0 6 0 <'s © cle ee Ce oe 0 8 6 68 eo 8 ws 6 0, 6 eo jo OR 8b Gg 6 68 & 6 6 0 0 6 8 eee 


ee oe WHEREOF., The parties hereto have set their hands the date herein 
named. 


PATIDEON CG see tener eee ecls evils: seed , 192 

5p Tae Paarl aaley 5 bil ae Meare or Nr me Re , County. 

Party of the First Part 
aes County Highway Commissioner i : 
y 
ee oT int sok 7 yt cea a Cin apa ae ge 
Soe ee eee ae. Ape oe eer 
dapat. ee Gad Fas ages eRe ae ee 
PN ER PO Ee 4 Sins Engineer """""" County Highway Committee 

I es a , 192.., for the ME TET eh oe Tk a ee 
WISCONSIN HIGHWAY COMMISSION 

Sn ea Party of the Second Part = 

By 


Pon A Behe Oe Caethlitese 3G CURSO Sysco ses (GNie OCIS ANC pCERC ORC Ta SUI St Te Jae Se ie ine VU A ea a a a} 


State Highway Engineer (Give Title or Position) 


120 CONCRETE PRACTICE 


CONTRACTOR’S BOND 


eevee ere ene eee rece ee Hho PDO eR eC Oe wee eo oe RAIL 6 5 6 6 6 1t 6 0 0 we 6 8 0 6b 6 ©) 6) 9) © ©) miele Opler) 6) 66) et Sse) ene 


Noe MRI rete Oe as Suret. areheld and: firmly bound Unto)cssei ene 
County, Wisconsin, in the penal BUDA, OF ois econ. Soc Syapie @ © 88 kis ae Sie een ea 
See te ep ois Gerdes eer Dollars ($......), lawful money of the United States, to be paid to said 


County, for which sum of money, well and truly to be paid, we bind ourselves, our heirs 
successors, executors, and administrators, jointly oe severally, firmly by these presents. 

Sealed with our seals and dated this........ day , 192. 

The condition of this obligation is such, that vf the said bounden principal shall, in all 
things, well and truly perform all the terms and conditions of the within and foregoing con- 
tract COMED Vae eee performed, and within the time therein mentioned, and shall pay to 
each and every person or party entitled thereto all the claims for work or labor performed or 
materials furnished for or in or about or under such contract as provided in Section 289.16 
of the Statutes, and shall have paid and discharged all liabilities for injuries which have been 
incurred in the said construction, under the operation of Sections102.01 to 102.34 of the 
Statutes, inclusive, and all acts amendatory thereto, then this obligation is void; otherwise 
it shall be and remain in full force and virtue. 


STATE OF WISCONSIN, 


om oe eee) 6 6 ow le 6 sible) © Ok ew) (elle alia Bae ee 


Ce 2 2 


County Ol Acai asic bee en nner take ies eae Principal 

ESSA rece OAL te Raa eed ke PI es hesrgat fn og eT iS) er A ae Ae te se notes 

being first duly sworn, on oathsays that heis 

worth. thesum of ...560605. 65 68 Weve coves or 0d Allah | © ieee Daye ss. Jo bau re eae) ee 
Surety 

Dollars in property within this state, over 

and above all debts, liabilities and exemp- 

tions. BY. ooo accia ts avs sabe ee ee ee 

Subscribed and sworn to beforemethis:.,. 0 9 © 2.22... serene 

Ody Olwcaenic ome ee eee, en eee , 192 In Presence: of, .10: 2 'ss.bus eee eee ee 


218 ele @ (0 (e188 6 "0 © © 50 (ev wc. 0 © Sis 6 + mm 


Notary Public. 


STATE OF WISCONSIN, 
Countyi0fse eo ee Le. eee Cee 


being first duly sworn, on oath says that he 
is. wortl (hersum Olsss. 6 eee eerie 
Dollars in property within this state, over 
and above all debts, liabilities, and exemp- 
tions. 


Subscribed and sworn to before me this.... 


Coeeeer eee re sneeereececeer eee 


Notary Public. 


NOTE—When executed by personal 
sureties make foregoing deposition. 


e098 Oe we ee 8 Oe ew Bo es se) 6 oes ae @ a bl ene’ ewe 


22 0 0 0 «6 8 ew im © 6 fe 19 We hw © 6 @ So lee hte ea) eee) eer ees 


NOTE—When executed by a Surety 
Company, attach to the bond certificates 
from the Insurance Department that Com- 
pany is authorized to transact business in 
the State, and that agent is duly licensed at 
the time; also a valid power of attorney of 
person or persons executing bond for the 
Company. 

The foregoing bond is hereby approved 


#0 8 0 60 6p 0. & © OOS) w Oe wees lel sw es" wi) eee el ie re rt 


District Attorney 


Exercises—What is the object of including the items B, C, D, and £ in 


the standard form of proposal? 


Prepare a form of proposal for a concrete sidewalk based on a lump sum 
for the job, with possible additions and deductions at certain prices per 


square foot. 


JOB 35. SPECIFICATIONS 


The specifications of a construction contract refer to the 
details of the relations and obligations of the owner, engineer, 
and contractor, and to the details of the work and method of 


construction. 


The first part is called the general specifications 


CONTRACTS, SPECIFICATIONS, AND PLANS 121 


or general conditions of the contract, and the latter part is called 
the detailed or technical specifications. 

General specifications include the following subdivisions. 

1. Definition. 

2. Rights of owner in.regard to inspection and supervision, 
right of access to work, changes, alterations, extra work, dis- 
crepancies, omissions, etc. 

3. Engineer’s or architect’s authority in regard to the work. 

4. Method of making estimates and payments for regular 
and extra work. 

5. Contractor’s responsibilities in regard to himself and 
workmen, compliance with laws, protection against damages 
and claims for labor and materials, assignments, subcontracts, 
time of completion, rate of progress, liquidated damages, pro- 
tection of work, defective work, delays, construction plants, 
sanitation, etc. 

Detailed or technical specifications include clauses specifying 
the kinds and quantities of the materials and the methods of 
doing the work. For example, technical specifications for a 
concrete sidewalk would include clauses in regard to the excava- 
tion, foundation, drainage, forms, kind and quality of the cement, 
sand, and stone, proportions of mix, consistency of mix, method 
of mixing concrete, method of placing concrete, method of finish- 
ing the surface, protection from weather, disposal of surplus 
material, and cleaning up. If not stated in another part of the 
contract, the length, breadth, and thickness of the walk should 
be given. 

When writing technical specifications, the first requisite is 
clearness. ‘The words, phrases, sentences, and paragraphs should 
be so selected and arranged that there can be no uncertainty as 
to the meaning of the specifications. The-use of ambiguous 
words and terms should be avoided. 

Specifications should be brief, but clearness should not be 
sacrificed for brevity. 

Indefinite, indeterminate, ambiguous, and arbitrary specifica- 
tions are to be avoided, as well as specifications which are 
unfair to the contractor or owner. 

Whenever practical, it is advisable to specify stock articles 
and sizes, as such are invariably cheaper than special articles 


122 CONCRETE PRACTICE 


and sizes. Special brands preferably should not be specified, 
unless the bidder is given a chance to suggest other suitable 
brands. 

A specification writer should be careful not to use parts of 
published specifications unless he is sure that these parts apply 
to the work contemplated. A study of published specifications 
is wise, but the blind copying of parts of these specifications for 
other work should be avoided. 

In determining the requirements for certain materials, it is 
often satisfactory to require them to pass certain well-known 
standard specifications and tests. For example, the portland 
cement used should be such as will pass the requirements of the 
A. 8. T. M. Standard Specifications for Portland Cement. 

In regard to writing specifications for methods of doing work, 
it is usually more satisfactory to leave the choice of methods to 
the contractor and then hold him responsible for the satisfactory 
performance of the work. If the method is specified and the 
work then turns out unsatisfactorily after the contractor has 
followed this method, he (the contractor) may escape the respons- 
ibility for the poor work. 

When writing specifications always examine each paragraph 
and clause to see if it represents good practice, if it applies to 
the work for which it is written, and if it is consistent and agrees 
in general with the other paragraphs and clauses with which it 
is to be used. 

Exercises—What are general specifications? What things do they 
include? 


What are detailed specifications? What do they include? 
Why is it sometimes not advisable to specify methods of doing work? 


JOB 36. STANDARD SPECIFICATIONS FOR A REINFORCED CON- 
CRETE HIGHWAY BRIDGE 

The following specifications are general specifications for 
all highway bridge work, and detailed specifications for 
concrete in forms prepared and used by the Wisconsin Highway 
Commission. 

Note that the general specifications have, on the first page, 
blank spaces, which are to be filled in with the name and general 
description of the job in question, and with a list of the plans 
included in the contract. 


: CONTRACTS, SPECIFICATIONS, AND PLANS 123 


In the detailed specifications for Concrete in Forms there are 
several clauses which may not be needed for certain jobs. For 
example, if all concrete was to be of Class A, clauses relating to 
Classes B, C and D would not be needed. Also, if a deck girder 
bridge were to be built, clauses relating to slab bridges and 
arches would not be required. 


WISCONSIN HIGHWAY COMMISSION 


being a part of contract annexed hereto. 
ihewore to be done under the contract shall be... 2... 20. cece cee ect cece ceccceveve 


See ere eee id see) Siew 66 6 ie 86 «a Sl 6 wet eC HHO Ae Rw KT Kee OO eK Ree CESS CCC eK BOC Cee eC Ree eH 
a ee ee eee Se ee Bae se sd we Se 6's 2 6 8 6 4 hw 6 eC ee CORO HCH SMO OME eee eMC HO KTH MKB ee KC MO Meee Ee CaS 
Siete eee eee ee eee ee SWE e) (pe (Cees — 26 eaters bis Oe ees a KO ee CU Dee ee He Ce nse Gee ea eewe res eer evnevacese 


ae wae ale) sé) ie) pe 6,05 1018 6 oe 6 66 6 Ce se wo Ce OCS TENS SORE CHM KS TeV EO CP e Se eraeecnsreveeve 


The plans mentioned in the contract are as contained in drawings prepared by the Wis- 
consin Highway Commission, and annexed hereto marked................00ce0eeeeeeee 


i ey 
sree eee eee ees es eee eee e eee eee eee eee sere reser eres eee eee eee eee eee eee eee eee ee eee eens 


Si i ee 2 


GENERAL PROVISIONS 


1. Work.—It is understood that the work to be done includes everything 
which might reasonably be considered necessary for a complete and work- 
manlike job in accordance with the plans and specifications in every detail. 

_ The Engineer will furnish and set survey stakes, or other marks at random 
distances from the center line of the contemplated roadway and furnish the 
contractor with a grade sheet showing the horizontal and vertical distances 
from said stakes or marks to the center of the roadway. The Contractor 
shall make such measurements, and set such stakes as may be necessary to 
begin work. He shall furnish all material, tools, machinery, labor and other 
means of construction to complete the work, including all excavation for 
foundations. He shall remove the structure existing at the site, or structure 
replaced by bridge mentioned in the contract, and pile the resulting material 
neatly on the bank. The excavations for foundations shall be according 
to the dimensions shown on plans and shall be carried to such depth as is 
necessary to secure good foundation free from all danger of damage from 
settlement, frost, or scour even though necessary to exceed the depth shown, 
but there shall be no variation in depth without a written order as herein- 
after provided. All excavated material and other obstructions to the stream 
bed at any point between the ends of the wings of the abutments shall be 
removed and the channel left clear and unobstructed. This includes the 
removal of any dirt in the banks of the stream necessary to give clear open- 
ing. Material suitable for back filling shall be placed in the fill back of the 
abutments. All foundation excavations in front of abutments and piers 
shall be refilled, all rubbish removed, and the bridge left in a neat condition. 


124 CONCRETE PRACTICE 


The Contractor shall notify the Engineer a reasonable length of time (not 
less than five days) in advance of the time when he expects to begin work. 
He shall give his personal attention to the work and shall not sublet the same 
without the consent of the Engineer. It is understood that good appearance 
and proper finish shall be considered as essential to the proper execution of 
the work. 

Until acceptance of the bridge, it shall be under the charge and care of the 
Contractor, and he shall take every necessary precaution against injury or 
damage to the bridge, or to any part thereof, by the action of the elements, 
or from any other cause whatsoever, whether arising from the execution or 
from the non-execution of the work. 'The Contractor shall rebuild, repair, 
restore and make good at his own expense, all injuries or damages to any 
portion of the bridge occasioned by any cause before its completion and 
acceptance. 

2. Time of Completion.—It is understood that the Contractor shall begin 
work at a reasonable length of time in advance of the time named for com- 
pletion, and prosecute the work with reasonable dispatch until the work is 
finished. 

If the Engineer believes that the work is unnecessarily delayed, he shall 
notify the Contractor and his sureties to the effect, in writing. If the 
Contractor, or his sureties, does not then, within ten days, take such meas- 
ures as will insure the satisfactory completion of the work, the Supervisors 
shall then have the right to order the Contractor to cease all work. The 
Contractor shall immediately respect such notice, stop all work, and cease to 
have any right on the ground. The Supervisors shall then take such means 
as may be necessary to complete the work. If the cost shall then be greater 
than the contract price, the Contractor shall pay such difference to the 
Supervisors, and his bond shall be security for his payment. 

3. Contractor’s Liability—The Contractor shall be liable for all accidents 
and damages that may accrue to persons or property during the prosecution 
of the work, by reason of negligence or carelessness of himself, his agents, or 
his employees. The work shall be conducted in conformity with all state or 
municipal laws and ordinances applying to the work, and precautions shall 
be taken to guard against accidents and loss of life. 

Before beginning work, the Contractor shall furnish the Supervisors with 
satisfactory evidence that he will be able to discharge all obligations result- 
ing on the work, through the operation of Sections 102.01 to 102.34 of the 
Wisconsin Statutes through authorized liability insurance, or that he has 
been exempted as provided in Section 102.28. 

4. Instructions to Foreman.—The foreman, or other person in charge of 
any particular portion of the work, shall receive and obey the instructions 
of the Engineer, relating to that particular part of the work, in case the 
Contractor is not present. Any foreman or workman employed by the 
Contractor on the work, who, in the opinion of the Engineer, does not 
perform his work in the proper manner, or who shall be disrespectful, 
intemperate, disorderly, or otherwise objectionable, shall at the written 
request of the Engineer, be forthwith discharged from the work, 


CONTRACTS, SPECIFICATIONS, AND PLANS 125 


5. Imperfect Work.—Any work or material which shall be imperfect, 
insufficient, or damaged by any cause whatsoever, shall, when pointed out by 
the Engineer or his authorized representative, be remedied immediately and 
made to conform with the plans and specifications. Any omission by the 
Engineer, or his authorized representative, to disapprove of, or reject, any 
such defective work or material, shall not be construed as an acceptance of 
the work, or as releasing the Contractor from remedying any defective work 
or material so as to conform to the plans and specifications. 

6. Bond.—In order to guarantee the faithful performance of the contract, 
and the payment of all lawful claims for labor performed and material 
furnished in and about the work done thereunder, the Contractor shall, 
before beginning work, and not later than fifteen days after the acceptance of 
this proposal, file a good and sufficient bond with the party of the first part, 
in the amount of the contract. The said bond shall be in compliance with 
the provisions of Section 289.16 of the Statute. 

7. Maintenance of Travel.—Unless the contrary is specified, such pro- 
vision to maintain travel during construction, as may be deemed necessary 
shall be made by the party of the first part. 

Where the road is required to be kept open to travel by the Contractor, 
the same shall be maintained in a safe condition and the Contractor shall be 
responsible under his bond for all accidents that may occur thereon due to 
the unsafe condition of the road. The Contractor shall be permitted to post 
such signs as may be approved by the Engineer warning the public of the 
probable increased danger due to construction. Until the work is accepted 
the Contractor shall take all necessary precautions and place proper guards 
for the prevention of accidents, and shall between sundown and sunrise 
maintain suitable and sufficient lights as warning signals. . 

Where the road is kept closed to travel, the Contractor shall erect and 
maintain a suitable barrier at each end of the work, and shall post such 
detour signs to direct the traveling public around the work as may be 
directed by the Engineer. 

8. Changes.—The Supervisors shall have the right to make such changes 
in the plans and additions thereto as may be necessary or desirable, and such 
changes shall not invalidate the contract. All such changes shall be ordered 
in writing by the Supervisors, and approved by the Engineer. Should such 
changes be productive of increased cost to the Contractor, a fair and equi- 
table sum, to be agreed upon in writing before such changed work shall 
have started, shall be added to the contract price, and in like manner 
deductions shall be made. 

9. Inspector.—The Supervisors shall have the right, if they so desire, to 
maintain an inspector on the work, who shall have access to all its parts. 

Inspectors shall be authorized to inspect all work done and materials 
furnished. Such inspection may extend to all or any part of the work and 
to the preparation or manufacture of the materials to be used. An inspector 
may be stationed on the bridge to report to the Engineer as to the progress of 
the work and the manner in which it is being performed. Also to report 
whenever it appears that the materials furnished and the work performed 


126 CONCRETE PRACTICE 


by the Contractor fail to fulfill the requirements of the specifications and 
contract, and to call the attention of the Contractor to any such failure or 
other infringement. Such inspection, however, shall not relieve the Con- 
tractor from any obligation to perform all the work strictly in accordance 
with the requirements of the specifications. In case of any dispute arising 
between the Contractor and the inspector as to materials furnished or the 
manner of performing the work, the inspector shall have authority to reject 
materials or suspend the work until the question at issue can be referred to 
and decided by the Engineer. 

The inspector shall perform such other duties as are assigned to him. 

He shall not be authorized to revoke, alter, enlarge or release any require- 
ments of these specifications, nor to approve or accept any portion of the 
work, nor to issue instructions contrary to the plans and specifications. 
The inspector shall, in no case, act as foreman or perform other duties for the 
Contractor, nor interfere with the management of the work by the latter. 
Any advice which the inspector may give the Contractor shall in nowise be 
construed as binding the Engineer in any way, or releasing the Contractor 
from fulfilling all the terms of the contract. 

10. Definitions.—The terms “Contractor,” “County,” ‘Supervisors ”’ and 
“‘Engineer” whenever used in connection with this contract shall be under- 
stood to have the meanings hereinafter stated. 

Contractor.—The person or persons entering into this contract as party of 
the second part acting directly or through a duly authorized representative. 

County.—The governmental unit or units entering into this contract, 
whether it be a County, City, Village or Town. 

Supervisors.—The duly authorized representatives of the said govern- 
mental unit or units in this contract. 

Engineer.—The State Highway Engineer of Wisconsin or his authorized 
representative. 

11. Referee.—It is mutually agreed by both parties to this contract that 
the Engineer shall act as referee in all disputes arising under the terms of the 
contract, between the parties thereto, and his decision shall be final and 
binding on both alike. 

12. Estimates——When provided in the contract, the Supervisors shall 
make advances to the Contractor at the intervals named. The amounts 
shall be certified by the Engineer to the Supervisors, and shall equal the value 
of the work done less 15 per centum. The granting of any such estimates 
shall not be construed as total or partial acceptance of any part of the work. 

13. Payment.—Upon the completion of the work, according to the con- 
tract, plans, specifications, and agreements as determined thereunder by the 
Engineer, the said Engineer shall make to the party of the first part a 
certified statement setting forth the work done by the Contractor, and the 
amount due him therefor. The obtaining of the certificate of the Engineer, 
as to the work done and the price therefor, shall be a Condition precedent 
to the right of the Contractor to be paid the sums due him under the terms 
of the contract. The Contractor shall pay all claims for work and labor 
performed and materials furnished in the execution of this contract provided 
in Section 289.16 of the Statutes. 


CONTRACTS, SPECIFICATIONS, AND PLANS 127 


CONCRETE IN FORMS 


206. Work.—It is understood that the work to be done includes everything 
which might reasonably be considered necessary for a complete and work- 
manlike job in accordance with the plans and specifications in every detail. 
The contractor shall perform all excavation and place concrete of the class 
indicated on the plans, or ordered by the engineer, for culverts, abutments, 
wing walls, end walls, catch basins, bridges, and other structures as directed 
by the engineer. All concrete placed in the work shall conform to the 
requirements for concrete of the class specified. All concrete and other 
masonry shall be built to the dimensions and contours shown on plans, with 
all reinforcement shown thereon. The engineer shall have the right to order 
the removal of any masonry not so built. The excavations for foundations 
shall be according to the dimensions shown on plans and shall be carried to 
such depth as is necessary to secure good foundation free from all danger of 
damage from settlement, frost or scour even though necessary to exceed the 
depth shown, but there shall be no variation in depth without a written order 
as hereinafter provided. All excavated material and other obstructions to 
the stream bed at any point between the ends of the wings of the abutments 
shall be removed and the channel left clear and unobstructed. This includes 
the removal of any dirt in the banks of the stream necessary to give clear 
opening. Material suitable for back filling shall be placed in the fill back 
of the abutments. All foundation excavations in front of abutments and 
piers shall be refilled, all rubbish removed, and the bridge left in a neat 
condition. 

207. Material.—Concrete shall consist of approved Portland cement, 
fine aggregate of sand, and coarse aggregate of broken stone or gravel, mixed 
in the proportions specified for the various classes given below. 

On request samples of all these ingredients shall be submitted to and 
approved by the engineer. 

208. Classification.—The proportions of concrete mixtures to be used in 
various parts of work shall be as specified on the detailed plans. The pro- 
portions shall be measured by volume, one sack of cement, weighing ninety- 
four (94) pounds net, to be considered one (1) cubic foot. In general, 
proportions shall be as follows: 

Class A.—Unless otherwise specified, Class A concrete shall contain one 
and one-half (114) barrels of cement per cubic yard of concrete. Proportions 
which will be satisfactory with well-graded aggregates are, approximately, 
one (1) part cement to two (2) parts fine aggregate to four (4) parts coarse 
aggregate. 

The following shall be the standard tolerances for grading of coarse aggre- 
gate. For the sizes two (2) inch to one-fourth (14) inch, twenty-five per 
cent (25%) to seventy-five per cent (75 %) of the total material shall pass a 
one (1) inch screen, not more than thirty per cent (30%) and not less than 
ten per cent (10%) of the total shall pass a one-half (14) inch screen, and 
not more than three per cent (3%) shall pass a one-fourth (14) inch screen. 
A tolerance of five per cent (5%) shall be allowed in the size of all screens. 


128 CONCRETE PRACTICE 


Class B.—Unless otherwise specified, Class B concrete shall contain one and 
one-quarter (114) barrels of cement per cubic yard of concrete. Proportions 
which will be satisfactory with well-graded aggregates are, approximately, 
one (1) part cement to two and one-half (214) parts fine aggregate to five 
(5) parts coarse aggregate. 

The following shall be the standard tolerances for grading of coarse 
aggregate. For the sizes three and one-half (314) inch to one-fourth (14) 
inch, twenty-five per cent (25 %) to seventy-five per cent (75 %) of the total 
material shall pass a one and one-half (114) inch screen, not more than 
twenty-five per cent (25 %) and not less than ten per cent (10 %) of the total 
shall pass a one (1) inch screen, and not more than three per cent (3 %) shall 
pass a one-fourth (14) inch screen. A tolerance of five per cent (5%) shall 
be allowed in the size of all screens. 

Class C.—Unless otherwise specified, Class C concrete shall contain one 
and five hundredths (1.05) barrels of cement per cubic yard of concrete. 
Proportions which will be satisfactory with well-graded aggregate are, 
approximately, one (1) part cement to three (3) parts fine aggregate to six 
(6) parts coarse aggregate. 

The coarse aggregate shall be graded as stated under Class B. 

Class D.—Unless otherwise specified, Class D concrete shall contain one 
and six-tenths (1.6) barrels of cement per cubic yard of concrete. Propor- 
tions which will be satisfactory with well-graded aggregates are, approxi- 
mately, one (1) part cement to two (2) parts fine aggregate to three and 
one-half (314) parts coarse aggregate. 

The following shall be the standard tolerance for grading of coarse aggre- 
gate. For the sizes one (1) inch to one-fourth (14) inch, twenty-five per 
cent (25%) to seventy-five per cent (75%) of the total material shall pass a 
one-half (14) inch screen, and not more than three per cent (3 %) shall pass a 
one-fourth (14) inch screen. A tolerance of five per cent (5%) shall be 
allowed in the size of all screens. 

By order of the engineer, the proportions of fine and coarse aggregate 
specified in the above classification may be varied slightly in order that a 
dense concrete with the specified content of cement may be obtained. If the 
engineer shall order, in writing, proportions differing in cement content from 
those specified, any suitable change thus necessitated and agreed upon in 
advance shall be made in the contract price. 

If the contractor shall use cement in excess of one hundred five (105) per 
cent of the specified amount in any day’s run, he shall receive no pay for the 
excess cement, if the contractor is furnishing cement, and if the state is 
furnishing it, the cost of the extra cement shall be deducted from the con- 
tractor’s estimates. . 

It is further specified that the price bid per cubic yard of concrete is to 
exclude the cost of the cement, and that a separate and distinct bid is 
required on the cost per barrel of cement in place in the work. The con- 
tractor, when the State does not furnish cement, in making his bid on cement, 
shall state, in addition to his price per barrel in place, the price per barrel of 
cement, f. o. b. destination which he used in figuring his bid, said price to be 


CONTRACTS, SPECIFICATIONS, AND PLANS 129 


exclusive of discounts. He shall also name the destination. In case the 
price per barrel of cement at said destination is more or less than the price 
used in the bid, due to changed price at the mill or changed railway freights, 
the said increase or decrease in price shall be added to or subtracted from the 
price bid on cement. 

If cement is furnished to the contractor by the Commission, said contrac- 
tor is not to include the price of cement (stated in the proposal) in his bid. 
In other words, he is to name a price per barrel for handling the cement only. 

209. Portland Cement.—All Portland cement used shall meet the require- 
ments of the standard specifications and tests for Portland cement adopted 
by the American Society for Testing Materials, and known as Serial Designa- 
tion C 9-21, together with all subsequent amendments thereto, and also an 
additional specification that when the cement is mixed in the proportion of 
one part cement to three parts standard Ottawa sand by weight, and cured 
one day in moist air, and two days in water, the average tensile strength of 
not less than three of these briquettes shall be equal to or higher than 150 
pounds per square inch. ‘The average tensile strength of standard mortar at 
seven days shall be higher than the strength at three days. 

All cement shall be properly protected against dampness and no cement 
shall be used which has become caked. Before the contractor shall be 
entitled to payment for the work, he shall present satisfactory evidence to 
the engineer that the full amount of cement required by the proportions 
specified for the work has been used. 

210. Fine Aggregate.—Fine aggregate shall consist of natural sand or 
screenings from hard, tough, durable crushed rock or gravel, composed 
preferably, of quartz grains, graded from fine to coarse, with the coarse 
particles predominating. Fine aggregate when dry shall pass a one-quarter 
(14) inch round opening; between twenty-five (25) and seventy-five (75) 
per cent shall pass a sieve, having twenty (20) meshes per linear inch; not 
more than twenty-five (25) per cent shall pass a sieve having fifty (50) 
meshes per linear inch; and not more than five (5) per cent shall pass a sieve 
having one hundred (100) meshes per linear inch. Fine aggregate shall not 
contain organic or other deleterious matter, not more than three (3) per cent, 
by weight, of silt. Routine field tests may be made on the fine aggregate 
as delivered. In case the laboratory test shows that it contains more than 
three per cent (3 %) silt by weight, the entire lot of fine aggregate represented 
by the sample shall be rejected. 

The percentage of silt, by volume, in the sand, may be determined from the 
colorimetric test, or, more accurately, in the following manner: Select two 
glass bottles, jars, or graduates which have uniform bore over a depth of 
eight (8) inches or more. The minimum diameter should not be less than one 
and one-half (114) inches. Select two representative samples of the material 
under test, each sufficient to fill a vessel to a depth of two and one-half (214) 
inches. Add enough water to make the total depth of the mixture of sand 

1 The twelfth paragraph under Clause 208 of “Concrete in Forms”’ shall 
not apply to bridge contracts. All bids for bridge work shall be a lump 
sum proposal as set forth in “Instructions to Bidders.”’ 


130 CONCRETE PRACTICE 


and water five (5) inches after shaking. Cover the top with hand or cork 
and shake vigorously for at least thirty (30) seconds. Hold the vessel in 
upright position, and tap its side with the finger to level the top of the sand. 
Allow to stand for one (1) hour. Then read the depth of silt to the nearest 
one-hundredth (14909) inch, and measure the total depth of sand and silt, 
making four measurements at different points around the container. By 
dividing the depth of the silt by the total depth of sand and silt, and multi- 
plying by 100, the percentage of silt by volume is found. If the average 
percentage of silt in the two bottles exceeds six (6), make a second determi- 
nation of the percentage of silt after the vessel and contents have stood for six 
(6) hours. In case the average result obtained after the sample has stood 
six (6) hours is still above six (6) per cent, the engineer may reject or at his 
discretion send a twenty (20) pound sample of the material to the laboratory 
for test. 

The presence of organic matter in the fine aggegate may be detected by 
the colorimetric test, which may be made as follows: Fill a graduated, wide- 
mouthed nursing bottle to the four and one-half (414) ounce mark with the 
sand under test. Add a three (3) per cent solution of sodium hydroxide, 
until the level of the liquid reaches the seven (7) ounce mark after the 
mixture has been shaken. After thorough shaking, allow the mixture to 
stand eighteen (18) to twenty-four (24) hours, and observe the color of the 
clear, supernatant liquid. If clear or of light straw color, the sand is free 
from harmful proportions of organic impurities. If the color of the liquid is 
dark amber to black, the sand shall not be used before it has been subjected 
to the standard mortar strength tests. 

Fine aggregate shall be of such quality that a mixture composed of one (1) 
part Portland cement and three (3) parts of fine aggregate by weight when 
made into briquettes shall show an average tensile strength at seven (7) 
and twenty-eight (28) days equal to or greater than the average tensile 
strength of briquettes composed of one (1) part of the same cement and three 
(3) parts standard Ottawa sand by weight. 

The percentage of water used in making briquettes of cement and fine- 

aggregate shall be such as to produce a mixture of the same consistency as 
that of Ottawa sand briquettes of standard consistency. The word “sand,” 
if used on plans or elsewhere, in specifying concrete proportions, shall be 
understood to be the fine aggregate as herein defined. 
_ The right is reserved by the State to forbid the use of fine aggregate from 
any plant when the character of the material in such plant, or the mode of 
operation in such plant is such as to make improbable the furnishing of 
reasonably uniform fine aggregate, free from clay, silt or loam. — 

211. Coarse Aggregate.—Coarse aggregate shall consist of clean, hard, 
tough, durable crushed rock or pebbles, having reasonably uniform gradation 
of material passing a screen having two (2) inch openings and retained on a 
screen having one-quarter (14) inch round openings. 

When the material is tested with laboratory screens it shall meet the 
following requirements: 


CONTRACTS, SPECIFICATIONS, AND PLANS 131 


Retained on a 2-inch (round openings) screen....... 0.00% 
Retained on a 1-inch (round openings) screen....... 30 to 70% 
Retained on a 14-inch (round openings) screen....... 70 to 85% 
Retained on a }4-inch (round openings) screen....... 100.0% 


A tolerance of five (5) per cent shall be allowed for wear in size of openings 
of all screens. 

Unless approved by the Engineer, no broken stone aggregate shall be used 
which has a French coefficient of wear less than six (6). 

The right is reserved to reject for cause any and all stone or gravel delivered 
on the work. 

Coarse aggregate consisting of crushed stone shall be of uniform character 
quarried from strata of approximately equal hardness, and the right is 
reserved by the State to forbid the use of crushed stone aggregates from any 
quarry when the character of the stone in the breast being operated and the 
mode of operation in blasting and handling is such as to make improbable the 
furnishing of uniform and graded crushed stone aggregate free from clay, silt 
or loam. 

The word ‘“‘stone,” if used on plans or elsewhere in specifying concrete 
proportions shall be understood to be coarse aggregate as herein defined. 

The right is reserved by the State to forbid the use of gravel pebble aggre- 
gate from any plant where the character of the material in such plant, or 
the mode of operation in such plant, is such as to make improbable the 
furnishing of hard and reasonably uniform well graded pebble aggregate, free 
from clay, silt or loam. 

212. Water.—All water used in concrete shall be subject to the approval 
of the engineer and shall be reasonably clear, free from oil, acid, alkali or 
vegetable substances and shall be neither brackish nor salty. 

213. Mixing.—The concrete shall be mixed in the quantities required for 
immediate use and any which has developed initial set, or which does not 
reach the forms within thirty (30) minutes after the water has been added 
shall not be used. 

Unless hand mixing is specially permitted by the engineer, the mixing shall 
be done in a batch mixer of approved type which will insure the uniform 
distribution of the materials throughout the mass so that the mixture is 
uniform in color and smooth in appearance. ‘The mixing shall continue for a 
minimum time of one (1) minute after all the materials are assembled in the 
drum, during which time the drum shall revolve at the speed for which it was 
designed, but shall make not less than fourteen (14) nor more than twenty 
(20) revolutions per minute. 

Where a fraction of a sack of cement is used the method of weighing or 
measuring shall be approved by the engineer. 

214. Hand Mixing.—When hand mixing is permitted it shall be done on a 
watertight platform. The fine aggregate and cement shall first be mixed 
until a uniform color is attained and then spread over the mixing board in a 
thin layer. 


132 CONCRETE PRACTICE 


The coarse aggregate which shall have been previously drenched, shall 
then be spread over the fine aggregate and cement in a uniform layer and the 
whole mass turned after the water isadded. After the water has been added 
the mass shall be turned at least four (4) times and more if necessary to make 
the mix uniform in color and smooth in appearance. Hand mixed batches 
shall not exceed one-half (14) cubic yard in volume. 

215. Retempering.—All mortar and concrete shall be used while fresh 
before the initial set has begun. No retempering of mortar or concrete shall 
be allowed. 

216. Consistency.—The consistency of the mix of the concrete shall be 
such that the mortar clings to the coarse aggregate. It shall not be suffi- 
ciently soft to flow rapidly or segregate. When the concrete is allowed to 
drop directly from the discharge chute of the mixer, the center of the pile of 
concrete shall flatten, but the edges shall stand up and not flow. The water 
shall be accurately measured and gauged and shall be automatically dis- 
charged into the drum with the aggregates. Quantity of water to be used 
shall be determined by the engineer and shall not be varied without his 
consent. 

217. Depositing Concrete.—Concrete shall be so deposited that the aggre- 
gates are not separated. Dropping the concrete any considerable distance, 
depositing large quantities at any point and running or working it along 
forms, or any other practice tending to cause separation of the aggregates 
will not be allowed. 

Throughout the placing of the concrete in the forms, the mass shall be 
puddled or spaded sufficiently to insure perfect contact and bond with 
the reinforcing bars, and perfect contact with the surfaces of the forms. 
Smooth, finished surfaces shall be obtained by working the finer materials 
against the forms. Faces which show in the finished work shall be true to 
form intended and shall be wholly free from swells, ridges, holes, cavities, 
mortar shortages and so forth. 

Wherever practicable, concrete shall be deposited continuously for each 
monolithic section of the work. All floors and other thin work shall be 
placed full thickness. 

All slab and deck girder spans shall be placed ee sas: to the top of the 
wheelguard in a single operation as outlined below, and the contractor shall, 
before beginning this part of the work, have sufficient material of all classes 
on the ground, adequate equipment, and the necessary labor force available 
to finish the work. On through girder and slab spans the forms for the 
railing shall be assembled sufficiently so that they can be set in place without 
delay. Concrete in the railings shall be poured the day after the concrete in 
the floor has been placed. 

Slab spans shall be placed in longitudinal strips. Concrete shall first be 
placed in the middle of the span and carried in both directions full height 
uniformly towards the ends of the span. Pouring shall commence at the 
curb and continue across the roadway. The width of strips shall be such 
that the concrete in any one strip shall not take its initial set before the strip 
adjacent is poured. In case the mixer is disabled, a vertical joint shall be 


CONTRACTS, SPECIFICATIONS, AND PLANS 133 


made parallel to the center line of roadway and enough concrete shall be 
mixed by hand to complete the strip. 

Deck girder spans shall be placed in longitudinal sections. Concrete shall 
first be placed in the middle of the span and carried in both directions full 
height uniformly towards the end of the span. Pouring shall commence at 
one curb and continue across the roadway. The width of sections shall 
extend between points midway between girders. In case the mixer is 
disabled, a vertical joint shall be made parallel to the center line of roadway 
and enough concrete shall be mixed by hand to complete the section. This 
joint is to be placed at the edge of one of the sections. To prevent a honey- 
combed bottom surface of the girders and before any concrete is deposited, 
not less than a three (3) sack batch of 1:2 cement grout shall be placed in the 
center of the girder. 

Concrete in walls shall be placed in continuous horizontal layers extending 
from end to end of the wall. Whenever Stops are made, the top surface 
shall be leveled off in a horizontal plane and grooved in the center with a 
4” 4” timber whose top face is flush with the concrete surface. The 
4”X 4" timber shall be removed as soon as the concrete has taken its initial 
set. When new concrete is placed on concrete which has a complete or 
partial set, the surface shall be thoroughly cleaned and scraped to remove all 
rubbish, badly cured concrete, laitance or other material detrimental to the 
finished work. The old surface shall then receive a coat of neat cement 
paste applied immediately in advance of the first batch. 

Bridge floors shall be built true to the dimensions shown on the plans, 
and the curbs shall be cast in the same operation as the balance of the floor. 
The curb forms shall be built to correct alignment and the contour of the top 
of the floor shall be determined by a strike board cut accurately so that the 
finished floor will conform to the dimensions shown on the plans. The top 
surface shall be floated to an even surface. Curbs shall be finished with a 
metal trowel and brushed. Corners shall be rounded with an edging tool. 
- Face of curbs shall be bricked. Sidewalks shall be metal trowled and 
brushed. 

Arch rings shall preferably be placed entire or, where this is not practi- 
cable, in monolithic rings with vertical joints parallel with the center line of 
the roadway, and each day’s work shall finish with one of these rings com- 
plete. Special care shall be observed to obtain good connection of spandrel 
walls to arch rings. 

Whenever concrete is desposited in freezing weather, special precautions 
shall be taken to avoid the use of materials containing frost, and thoroughly 
effective means shall be used to prevent the wet mixture from chilling or 
freezing. The water should be boiling and the aggregate heated to a 
temperature of not less than one hundred fifty (150) degrees Fahrenheit 
before the ingredients are placed in the mixer. The concrete shall be placed 
in the forms immediately after mixing. 

The entire work shall be covered in such a way as to retain the heat and 
prevent freezing of concrete in the wall. The use of salt to prevent freezing 


134 CONCRETE PRACTICE ; 


shall not be allowed, and all concrete placed in freezing weather shall beat 
the contractor’s risk. 

Concrete may be deposited through water only by special authority from 
engineer, and that in writing. When so deposited it shall be by means of one 
or more tremies or chutes. ‘The lower ends shall be placed on the bottom of 
the foundation and the tremie kept filled, concrete escaping from the bottom 
because of a slight raising of the tremie. The surface of the concrete shall 
be kept level, and the work having once been started, shall be carried on 
continuously until that portion of the foundation to be deposited in water is 
completed. When the work is continued, the water shall be exhausted and 
the surface cleaned as hereinbefore described. The contractor shall have 
sufficient material on hand and labor available to guarantee that this can be 
done. The tremie shall be charged in such a way that the cement is not 
washed out of the concrete, and whenever the charge is lost, it shall be 
recharged in the same manner before placing is continued. In all cases 
where concrete is deposited through water, as hereinbefore described, the 
same shall be a Class A eee No concrete shall be poured unless an in- 
spector is present. 

218. Forms.—All forms shall be built tight and substantial, so as to retain 
the finer parts of the concrete mixture, and to hold rigidly to place until the 
concrete has set. Forms which have sagged, bulged, or become warped 
or distorted in any way shall immediately be removed and the concrete 
affected thereby replaced with fresh concrete. The engineer shall have the 
right to require forms to be held in place by means of rods and waling strips. 

All lumber used for surface forms shall be of anevensurface. Where the 
concrete will be exposed to view, the forms must be built of selected lumber, 
sized and dressed, and free from defects which will show in the finished work. 
All joints shall be neatly fitted; triangular chamfer strips shall be carefully 
fitted with mitred corners. 

The forms for all concrete girders, railings, and arch spandrels shall be 
built with especial care from selected lumber, which shall have been carefully 
cut, planed and fitted in a planing mill, in such a way that the finished 
concrete work shall be of the exact dimensions shown on the plans. These 
forms shall be set up entire, firmly braced and inspected by the engineer 
before any concrete is placed in this part of the work. 

In framing centering for arches, allowance shall be made for settlement of 
centering, deflection of the arch after removal of centering and permanent 
camber. Centers shall be framed for a rise of arch 34 ¢ of an inch for each 10 
feet in span greater than the rise marked on the drawings. The centers shall 
be so designed as to be rigid in place and free from all sagging and bulging. 
No concrete shall be poured until the engineer has inspected the centering 
and passed on its sufficiency. 

Effective means shall be used to prevent the adhesion of the concrete to the 
forms. The inside surfaces of all forms for girders, railings, or arch spandrels, 
or any other ornamental work, shall be well covered with shellac or a light 
oil one day before the concrete is placed. . 


CONTRACTS, SPECIFICATIONS, AND PLANS 135 


Before concrete is placed, the forms shall be thoroughly wet and cleaned 
of all accumulations of rubbish. Care shall be observed to insure that the 
forms are cleaned in advance of pouring, from all dirt, or concrete which may 
have spattered and dried on the inside of the forms. 

In structures six (6) feet in span and under, the year of construction is to be 
stamped into the concrete on one end face of one wing wall or end wall in such 
a position as to be readily accessible for inspection. 

219. Removal of Forms.—In order to make possible the obtaining of a 
satisfactory surface finish, forms, on ornamental work, railings, parapets, 
and vertical surfaces that do not carry loads and which will be exposed in the 
finished work shall be removed in not less than four (4) nor more than forty- 
eight (48) hours, depending upon weather conditions. Forms under slabs, 
beams, girders, and arches shall remain in place at least twenty-one (21) 
days in warm weather, and in cold weather at the discretion of the engineer. 
Forms shall always be removed from columns before removing shoring from 
-beneath beams and girders, in order to determine the conditions of column 
concrete. 

The removal of forms before the concrete has sufficiently set shall not 
relieve the contractor of responsibility for the safety of the work. As soon 
as the forms are removed all rough places, holes, and porous spots shall be 
filled, and all bolts, wires, or other appliances used to hold the forms and 
which pass through the concrete shall be cut off or pushed back with nail 
set one-half (14) inch below the surface and the ends covered with cement 
mortar of the same mix as used in the body of the work. 

As soon as the forms are removed from the base rail, coping or other 
ornamental work, the construction joints shall be opened and the edges 
beveled back sufficiently to prevent breakage at the junction points; the 
concrete shall be beveled back not to’ exceed an eighth of an inch both sides 
of all expansion joints in ornamental work. 

On spans carrying baluster railing, the centering shall be removed before 
the top rail of the railing is placed. 

220. Surface Finishing.—The contractor shall build the forms, and place 
the concrete, in such a way that a smooth, even surface will be presented 
on removal of the forms, and the work of finishing thereby reduced to a 
minimum. . 

All concrete surfaces shall be well spaded by forcing a flat blade spade 
vertically down between the concrete and the form, and then by pulling the 
top of the spade away from the form so that the mortar will in all cases flow 
to the face of the forms. 

The rubbed finish shall be made by carefully rubbing the surface with a 
fine carborundum brick, immediately after removing the forms. The first 
step in this process is to moisten the surface with water, immediately follow- 
ing with the fine carborundum brick, rubbing in a circular motion. Only 
light pressure should be applied and the rubbing continued until all the air 
holes and small depressions are filled, and an excess of mulch is on the 
surface. The mulch should then be brushed out smooth with a long bristle 
paint brush. 


136 CONCRETE PRACTICE 


After the concrete has been rubbed smooth and has set for a period of from 
five (5) to eight (8) days, it shall then be again rubbed, using a carborundum 
brick. Rubbing shall be continued until a smooth surface free from lumber 
marks and irregularities is obtained. In using carborundum brick, the 
surface to be rubbed may be moistened with water to facilitate the rubbing; 
the fine material loosened by the brick may be used to fill the pores in the 
concrete. On warm days when the sun is quite strong, rubbed surfaces 
should be covered with canvas to keep the sun from drying out the surface 
too rapidly, thus causing checking. 

Before final acceptance all dust left on finished surfaces by the action of 
brick shall be removed by rubbing with canvas, when the surface is perfectly 
dry. 

221. Concrete Balusters.—The concrete in concrete balusters shall consist 
of a mixture of one part of cement, one-half of which is white cement, and 
two parts fine aggregate. 

The fine aggregate shall conform to the specifications for fine aggregate in. 
concrete pavements. 

The aggregate shall first be very thoroughly mixed in a dry state by shovel- 
ing on a tight board for not less than ten (10) minutes. The water shall then 
be added to produce a concrete of the consistency specified elsewhere in these 
specifications. After placing in the forms, the concrete shall be tamped with 
unusual care in order to insure that no voids remain and that the air pockets 
on the surface of the balusters are reduced to a minimum. 

After brushing, the balusters shall be carefully stored, sheltered from rain, 
sun or other damage, and cured under a damp canvas for a period of at least 
six (6) days. 

At the time the concrete baluster has reached the proper degree of set 
(approximately ten (10) days after pouring) it shall be carefully rubbed to a 
smooth, even finish with a fine-grained carborundum brick. 

All balusters shall be manufactured by skillful, experienced workmen, and 
no imperfect cracked or damaged balusters will be accepted. 

222. Curing Concrete.—Careful attention shall be given by the contractor 
to the proper curing of the concrete. Handrails, floors and troweled sur- 
faces shall be protected from the sun, and in drying weather the whole 
structure shall be kept wet for a period of one (1) week. Concrete floor slabs 
may be covered with damp sand as soon as the concrete has taken its initial 
set and then kept wet for one (1) week. Other precautions to insure thor- 
ough curing of the concrete shall be taken by the contractor as directed by 
the engineer. The roadway shall be kept closed to traffic for three. (3) weeks 
or if in the opinion of the engineer the weather conditions make it advisable, 
the roadway may be opened to traffic in a shorter or longer period of time, 
provided the closed period shall never be less than two (2) weeks after the 
concrete is deposited. 

223. Foundation for Concrete.—Where concrete is to rest on any exca- 
vated surface other than rock, special care shall be taken not to disturb the 
bottom of the excavation, and the final removal of material to grade shall not 


CONTRACTS, SPECIFICATIONS, AND PLANS 137 


be made until just before the concrete is laid, except in concrete foundations 
for pavement. 

The excavation lines and bases of structures shown on the plans shall be 
considered only as approximate and they may be ordered in writing by the 
engineer to be placed at any elevation or of any dimension that will give a 
satisfactory foundation. Any additional concrete that may be required by 
the engineer below or beyond the line shown on the plans shall be paid for at 
the contract price. No structure shall be commenced without the engineer’s 
approval. All rock or hard pan foundation surfaces shall be freed from loose 
pieces, cut to firm surfaces, and cleaned to the satisfaction of the engineer 
before laying concrete. All seams shall be cleaned out and filled with con- 
crete or mortar, and payment for such concrete used in filling shall be made 
at the contract price for the class of concrete used. 

224. Measurement and Payment.—The quantity of concrete to be paid 
for shall be the number of cubic yards under the various classes measured in 
place in the finished structure placed in accordance with the plans, or as 
ordered by the engineer. No payment will be made for any concrete outside 
of these limits nor for any concrete whose replacing is rendered necessary 
owing to lack of proper care, and the price paid per cubic yard shall include 
all materials, forms, labor and other incidental expenses necessary to satis- 
factorily complete the work as specified in the foregoing paragraph. Unless 
otherwise stipulated all excavation required for placing concrete shall be 
included in the price bid for concrete. 


Exercise.—If a reinforced concrete slab bridge was to be built of Class A 
concrete in Wisconsin during July and August, what clauses in the detailed 
specifications for Concrete in Forms would not be needed? 


JOB 37. PLANS 


Plans and drawings are used as a part of a complete contract 
to help the parties to visualize correctly the structures. Many 
details that are very difficult to describe with words are easily 
shown by means of drawings. 

In general, the complete plans for a concrete building may show 
the location of the lot, including its dimensions and boundaries 
and sometimes contours; basement, floor, and roof plans; eleva- 
tions; framing plans; sections; and details. In addition to these, 
there may be plans for plant layout, forms and framing, rein- 
forcement bending, various details, etc., according to the Judg- 
ment of the engineer or architect and the needs of the contractor. 
Plans for a concrete arch bridge would include the site, plans, 
elevations, stress sheet, sections, and details. 

The scales used for plans vary greatly, depending on the job in 
particular, and the opinion of the engineer or architect. Scales 


138 CONCRETE PRACTICE 


of 14 or 1g in. to the foot are common for general ache and 34 or 
1! Ve in. to the foot for details. 

When obtaining dimensions from plans, the distances given in 
figures will usually take precedence over the scaled distances. 
Tracing cloth, drawing paper, and blueprint paper often shrink a 
little with age, so that drawings which scale correctly when they 
are made will not scale correctly a few months later. 

In most drawings, various symbols are used to take the place 
of words. ‘The selection and use of symbols vary somewhat in 
different localities, in different offices, and with different trades. 
Some of the common symbols used in concrete work are: 


Ge means 6 in. 3’ means 3 ft. 
40’’ means 4 sq. in. 2'O’ means 2 sq. ft. 
16’’@ means -in. round rods ¢ means center line. 


34 4’'(A means 34-in. square rods 
3” o.c. or 3’’c.c., means that rods are spaced 3 in. on centers or from 
center to center. 


Common abbreviations for words such as lb. for pounds; in. for 
inches; ft. for feet; M for thousand; squares for 100 sq. ft.; sq. ft. 
for square feet; cu. ft. for cubic feet; sq. yd. for square yard; cu. 
yd. for cubic yards; bd. ft. for board feet; etc., are also used in 
concrete work. 

When reading plans and blueprints, information for some 
particular item is usually wanted in regard to its location, dimen- 
sions, kind, finish, or quantity. Reading of plans and blueprints 
is not very difficult, but it does require careful attention to detail, 
especially upon the part of a beginner. Anyone who has com- 
pleted a drafting course in school, or who has had some experience 
in a drafting office, should have no difficulty in reading and 
understanding the average structural drawings. Drawings that 
are incomplete, inaccurate, or otherwise poorly drawn will cause 
trouble for any plan reader, quantity surveyor, estimator, or 
constructor. Plan reading is simply the examination of the 
drawing or blueprint, to secure some information that is shown in 
the drawings or blueprints. 

In the following job, there are complete plans for a reinforced- 
concrete slab highway bridge. An examination of these drawings 
will bring out much information in regard to plans for concrete 
work, especially if the questions in the following job are carefully 


CONTRACTS, SPECIFICATIONS, AND PLANS 139 


answered. Ina later job, a quantity estimate has been prepared 
for this particular concrete structure. Checking this quantity 
estimate against the plans and specifications will give the average 
student a good understanding of what is meant by plan and 
blueprint reading. 


Exercises.—What are plans or drawings? 

What is the object of making drawings for a concrete structure? 

Name the drawings which, in your opinion, should be provided for a one- 
story concrete garage with basement. 

What scales would you use in preparing the general and detailed drawings 
for this garage? 

What is plan reading? 


JOB 38. STANDARD PLANS FOR A REINFORCED CONCRETE 
HIGHWAY BRIDGE 


The plans shown in Fig. 71 are standard plans for a reinforced 
concrete slab highway bridge, with a clear span of 16 ft. and a 
28-ft. roadway. ‘These plans contain a half-side elevation, a 
half section just inside a rail, a half-end elevation, and a half 
section through the paneling at the center of the span, as well as a 
bill of reinforcing steel, a detail of the drain, general notes, and 
estimated quantities. 

In Fig. 72, are shown the horizontal plan, front elevation, end 
view of a wing, and sections of a reinforced concrete abutment 
suitable for the slab bridge shown in Fig. 71. Note that. several 
dimensions are omitted in the abutment plans. These dimen- 
sions are to be filled in when the height of the abutments, width of 
roadway, clear span, and depth of the reinforced concrete slab 
bridge have been determined for the particular job in question. 


Evxercises.— Using the bill of bars, check the total weight of reinforcing steel 
required in the plans for the reinforced concrete slab bridge shown in Fig. 71. 

What would be the required width of the bridge seat in the abutment 
plans of Fig. 72 to care for the slab bridge of Fig. 71. 

What would be the required depth of the bridge seat notch? 


JOB 39. PLAN READING 


Plan reading is simply examining the plans to secure some 
desired detailed information. Any person who can read English 
fairly well, and who will pay careful attention to details, should 
not have much difficulty in learning to read plans. 


CONCRETE PRACTICE 


140 


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CONTRACTS, SPECIFICATIONS, AND PLANS 


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142 CONCRETE PRACTICE 


The following questions and answers in regard to the reinforced 
concrete slab bridge, shown in Fig. 71, will illustrate to some 
extent what is meant by plan reading. 


Question: What is the depth of the slab at the center of the roadway? 

Answer: From the half-end elevation, the depth is shown to be 1 ft. 2 in. 

Question: What is the depth of the slab near the rail? 

Answer: From the half-end elevation or the half section A-A, the depth is 
shown to be 1 ft. 1 in. 

Question: How far above the bottom of the slab is the main tensile rein- 
forcement (7-in. round bars) placed? 

Answer: From half section A-A, the centers of the %-in. round bars are 
to be 17% in. above the bottom of the slab. 

Question: What is the total length of the slab? 

Answer: From the half-side elevation and the half section A-A, the total 
length of the slab is 18 ft. 6 in. 

Question: What is the total overall length of the bridge? 

Answer: From the half-side elevation and the half section A-A, the total 
overall length of the bridge is 18 ft. 6 in. plus 4 in., or 18 ft. 10in. The ends 
of the rail extend 2 in. beyond each end of the slab. 


Exercises.—Where are the drains placed? 
How many drains are required? 
How many main reinforcement bars (7-in. round bars) are ‘required? 
What is the total width of the top part of the bridge rail? 
_ How high is the bridge rail above the curb? 
How high is the curb? 
How wide is the curb? 
Are there any sidewalks provided on this bridge? 
Where are the expansion joints located? 
What are the dimensions of the recessed panels in the bridge rail? 
How many of these recessed panels are there? 
What is the spacing of the main reinforcement bars (7-in. round bars) in 
the floor slab? 
What is the total number of bends to be made in these 7-in. round bars 
in the floor slab? 
What is the spacing of the transverse reinforcement (14-in. square bars) 
in the floor slab? 
How far from the center of the slab are each of the three bends of the %-in. 
round bars made? (See half section A-A.) 
What are the dimensions of the notch left in each end of the bridge floor 
slab for the concrete pavement? 
What kind of reinforcement bars are required? (Plain or deformed?) 
What kind or class of concrete is required? 
What is the ‘“‘crown” in inches provided in the center of the bridge floor 
slab? 
What is the total overall width of the bridge? 


SECTION IV 
ESTIMATING 


JOB 40. ESTIMATING IN GENERAL 


The work of estimating is commonly divided into two parts: 
(1) estimating quantities or “taking off,” and (2) estimating unit 
costs. 

A simple concrete job may be divided into the following parts 
in regard to quantities and units: 

. Excavation in cubic yards. 

. Forms and false work in square feet of form surface. 
. Concrete in cubic yards. 

. Steel in pounds or tons. 

. Finishing in square yards. 

. Cleaning up for job. 

For a more complicated job, such as a reinforced concrete 
building, other items should be added, as masonry (brick, stone, 
terra cotta) in cubic feet or per thousand brick or block; lath and 
plastering in square yards; building trim, windows, and doors; 
hardware; iron work; roofing in squares of 100 sq. ft. or sq. yd.; 
flashing; painting in square yards; sundries; subcontracts; and 
general overhead (if not previously apportioned). 

Each of these divisions may be subdivided into the following 
_ parts: 

a. Material in units suitable for each kind of material. 

b. Labor in hours. 

c. Plant in hours or days. 

d. Overhead in hours. 

Sometimes an estimator will use the subdivisions a, b, c, and d 
as the main divisions and then use the divisions 1, 2, 3, 4, etc.; 
as subdivisions. 

A complete estimate of the quantities of materials may be said 
to be a “quantity survey. In some localities the ‘quantity 
surveyor” prepares a list of materials for any given Job and all 

143 


Oot WN & 


144 CONCRETE PRACTICE 


contractors, who bid on the job, use this list. The contractors 
make their own individual estimates for labor, plant, and 
overhead. 

The preparation of a list of materials is known as the “take 
off.” The estimator tabulates all of the different materials as 
to kind, number, size, weight, volume, or other units used. The 
selection of units for different materials will be explained in 
more detail in later jobs. 

In estimating the quantity of labor for a given job, the total 
number of labor hours or man hours for each class of labor and 
each kind of work is tabulated. It is often difficult to estimate 
accurately the number of hours required for a laborer to perform 
a given task, as some laborers work faster or slower than the 
average. When a contractor has had practically the same gang 
working for him for a few months, his experience will enable him 
to estimate quite closely as to the amount of work this particular 
gang will do in a day or an hour. 

The selection of the plant will often depend on the machinery 
that the contractor has available for the job. The estimate of 
the time that the plant will be used may be based on the total 
time that the plant is held available for the job, or on the total 
time that the plant is run, or on both. 

The estimate of overhead may be given in hours or days that 
will be required of the superintendent, engineers, inspectors, 
clerks, stenographers, watchmen, etc., to care for the work of this 
particular job. 

When estimating unit costs, the costs of the materials at the 
job are usually computed. This cost includes first cost, freight, 
_unloading, cartage, storage, inspection, testing, and insurance. 

Total labor costs are found by multiplying the hours estimated 
for each class of labor by the corresponding wage rate per hour, 
and then adding results. 

Plant costs usually include cost of installation, maintenance, 
operation, removal, interest on investment, and depreciation 
(proportionate part of first cost of plant). These costs often 
include the labor costs of machine operators, such as hoisting 
engineers, firemen, etc. To get unit costs, the total cost of the 
plant on the job is computed and divided, either by the total ~ 
number of hours that the plant is held available for the job, or — 


ESTIMATING 145 


else by the number of hours that the plant is actually operated 
on the job. Some estimators use two plant hour rates; one when 
the plant is idle, and another when the plant is running. 

Overhead costs include such general office and other labor costs 
that are not considered as direct productive labor on the job. 
Other overhead costs are insurance, rents, office stationery, 
expense of plans and specifications, interest, legal expenses, travel- 
ing expenses, sundries, etc. ‘These overhead expenses are often 
apportioned to the several parts of the job according to the labor 
hours or labor costs of these parts, though sometimes some of the 
overhead costs are assigned to the materials and plant. 

Last, but not least in importance, is the profit. The amount of 
profit is usually expressed as a percentage of the total cost of the 
job. This percentage usually varies from about 8 to 15 per cent, 
depending on the contractor’s desire for the work, what he thinks 
is fair, and what he thinks he can get. For small jobs, 15 per 
cent is a common figure for profit with 12!4 per cent for medium 
jobs, 10 per cent for large jobs, and possibly 8 per cent for very 
large jobs. The percentage of profit added also depends, to some 
extent, on how often payments are to be made and in what 
amounts. On large jobs, payments up to about 85 per cent of 
the total work done are made each month. 


Exercises —Name the six main divisions of concrete work. 

Name the four subdivisions. 

What is a “quantity survey” and how is it made? What is a ‘‘take off?” 
What things are usually included in material costs? 

What is meant by overhead and what does it include? 


JOB 41. ESTIMATING EXCAVATION 


While it is comparatively easy to compute the quantities for 
excavation, there are several items which will affect the total 
labor required and the costs. 

Excavation is usually divided into two classes: (1) general 
excavation, such as excavating for a large cellar or making a cut 
for a railroad or a highway; and (2) particular or special excava- 
tion, such as digging narrow trenches, footing holes, ete. Gen- 
eral excavation may be done by hand, scrapers and horses, or 
steam shovels, while hand work is practically always required for 
special excavation. 


146 CONCRETE PRACTICE 


The time and cost of excavation also depends upon the charac- 
ter of the material to be removed. A cubic yard of hardpan may 
require from two to four times as much labor as a cubic yard of 
loam. 

In computing quantities for excavation, the estimator must 
be careful to include the dimensions from outside to outside of 
footings, and from the top of the grade to the bottom of the base- 
ment floor. 

In the ‘‘take off,’’ each item of general and special excavation ° 
must be listed separately, with dimensions and quantities, as 
well as the kind of soil. Sometimes the earth will retain its verti- 
cal position without support. In other cases, the earth walls 
will require sheeting or bracing. In general excavation with 
steam shovels, it is sometimes more economical to omit the 
sheeting and slope the banks. 

When computing quantities where the surface of the ground is 
sloping or uneven, the horizontal projection may be divided 
into a number of convenient squares and rectangles, and the 
average height of each section estimated. | 

The following table gives the angles of repose for various kinds 
of earth: 


ANGLES OF REPOSE 


Angle with horizontal in 


; degrees 
Material 


Dry | Moist Wet 


30-45 20-40 
week ae a aoe CER aes Setar Pee ets ey eee 25-45 25-30 


C1 Ve OO 6 Oe wm B00. ete 6 ce 0 16. & 8 co '8\ ‘B61 \6 © Ole) (6. exe 


Slap ne “ec ew eb O28) ee) ee) We Oe 6 


The work of excavation done per man per hour varies greatly 
with the skill of the laborer, his inclination to work, and the 
character of the soil. The following tables give approximate 
values: 


ESTIMATING 147 


SHOVELING—CuBIC YARDS PER MAN PER Hour INCLUDING LOOSENING WITH 
Picks AND SHOVELING INTO WAGONS oR TRUCKS 


Total lift not more than 6 ft. 


General excavation 


220 phe ae 20 ie een Si ee Me, Special 
Material Dry Wet ee 
Cubic yards per hour 
So APO 0 0.60-1.60 | 0.50—-1.00 | 0.30-0.70 
ead EEL sie. d's dot ses 0.40-1.00 | 0.25-0.50 | 0.20-0.40 
ieaepOLIANC. CIAY) ..). 6... 2... ku 0.30—0.60 | 0.20-0.40 | 0.15-0.35 


ST ela Cin 0.25-0.50 | 0.15-0.35 | 0.10-0.30 


SHOVELING LOOSENED MaTERIAL—CuBIC YARDS PER MAN PER Hour WHEN 
SHOVELED INTO WAGONS OR TRUCKS 


Total lift not over 4 ft. 


Material Cubic yards 
per hour 
Preece Ontaenr ExXCAVAUION. . 2.2.0... bea ee es 0.90-1.75 
PTET OMEOIIWEXCAVATION... 04.606. ee wey eee eee 0.85-1.65 
Pea eee Cee ayn EXCAVALION..; 02. ca. ee pees 0.60—1.30 
Pee Pe KCAVAUON 1. cs ec ws ce bee ce eee 0.50—-1.20 
eee IMPrOTOreTONGU LO WOCON . 2... ca. es cca eee tee ele hee 2 .00—4 .00 
Stone and gravel from ground to wagon................ 1.50-3.50 
Peer eeOMO TOU GOLWAdON.... oo. cre tn ee Oe ee bam ee 1.50—-4.00 


A driver and helper with two horses and a plow can loosen from 
15 to 40 cu. yd. of earth per hr. depending on the character of the 
soil. Heavy soil may require four horses. 


CAPACITIES OF VEHICLES 
Ordinarily taken as 80 per cent of rated capacity 


Vehicle Cubic yards 
RRR oa ernie acc g soe 4 ial'o, dees gun Bao as 0..10-0 7.15 
Reine VE te Coir 2S ye ahh. s ie cp eiiess soe ve ols plcaren © a's 0.10-0.25 
Oe LETELR CET Cayce ae a ee 0.35-0.65 
Pe OTSCVOUINPI WHEOD 08. 1. eu Phew ow ae lian 1.00-1.75 


Dh CR, “0 US DRE SS a a He ge Gn 1.00—5.00 


148 CONCRETE PRACTICE 


EconomicaL Haut (APPROXIMATE) 


Vehicle Distance 
Wheelbarrows Sunes ce oe ne ee Not over 100 ft. 
Drag scrapers; ccs ore eee Not over 150 ft. 
Wheel scrapers tcsvhicieuiin ks ten ee Not over 500 ft. 
Dump Wagonses fal feo ue his eee 500 ft. or over 
Auto TPUcks ee le fe ha ey ne Oho I he een 1000 ft. or over 


TIME FOR HAULING 


| Load, Unload, -3| eee 
Vehicle : ; travel, miles 
minutes minutes 
per hour 
Wheelbarrow.5 28 e152. ka. 1.00— 3.00 0.20 2 
rae sera pera. = ee ee 0.25- 0.50 0.25 2 
Wheel scraters tia. mxhee ae 0.25-— 0.50 0.25 2 
Dump wWag0lay ee eeee es 1.00- 9.00 | 0.25-1.00 2 
Auto truck saeny cer oe eae 1.00-12.00 | 0.25-1.00 8-15 


Time required to load a wheelbarrow depends on whether one 
or two men are shoveling, and on the kind of material. 

Time required for loading a dump wagon depends on number of 
shovelers in hand loading, on operation of shovel in machine 
loading, and on conditions of work. 


GASOLINE OR STEAM SHOVEL CAPACITY 


Size of shovel, cubic yards Cubic yards per minute 


34 1.00— 2.50 
1% 1.50— 4.00 
114 2.00— 5.00 
134 2.50— 6.00 
2 3.00— 7.00 
21 4.00— 9.00 
3 5.00-11.00 


The output of a steam shovel per minute depends on the amount 
of moving it must do, the time required to move the loaded 
truck and place an empty truck in position, the skill of the 
shovel operator, the speed of the shovel, and the character of 
the soil. Hence, all figures given above are approximate. Steam 


ESTIMATING 149 


shovels are often not economical when the amount of general 
excavation is less than about 1500 cu. yd. 


BacKFILLING—CuBIc YARDS PER Man PER Hour WHEN MATERIAL Is 
SHOVELED INTO TRENCH AND TAMPED A LITTLE 


Cubic yards per hour 


Material 
per man 
Sos dai, | Se eee 1.5-3.0 
Br IA ER ck Se es ee ee 1.0-2.5 
PRE PTPPOUP GO OIAYS fii ced bee een 0.8-2.0 


When the backfill material has to be wheeled, the amount of 
backfill per man per hour will be reduced proportionately. 

Sheeting and bracing for trenches is usually estimated by the 
square foot of surface measurement of the earth retained. The 
amount of lumber in board feet for sheeting may vary from about 
100 to 400 bd. ft. per 100 sq. ft. of surface measurement of 
retained earth. The cost of lumber for trench sheeting may vary 
from about $35 to $60 a thousand board feet. When the trench 
sheeting can be removed and used again, the wastage of lumber 
varies from about 20 to 50 per cent. One man will place from 7 
to 10 sq. ft. of sheeting per hour and remove from 20 to 40 sq. ft. 
per hour depending on the depth of the trench. 

The cost of labor per hour varies greatly in different localities 
and in different years, so that a knowledge of the local labor supply 
is essential in preparing a cost estimate. The following approxi- 
mate values in preparing a cost estimate will be used: 


Wage or cost per 


Kind of labor hour, dollars 


erp ae Se es ae fs wins ¥oe WN Sane oa 0.40—0.60 


ee ae Be ies oc. 8858 G sau age eS PS KB 0.80-1.40 
Tear RNs. y God coef lil erscyicpea a Y ode ed oma ues 1.00-1.50 
Man and team with scraper or wagon................ 1.00—1.50 
Ey EGS be 0 oe) 2.00—-5.00 
ire novel. Witt ODCYTALOL<... 5.4.2. uc sleet wee nee 2.50-7 . 50 


Illustrative Problem.—Prepare an estimate of cost of excavation of 
20,000 cu. yd. of general excavation, 400 cu. yd. of special excavation, 
300 cu. yd. of backfill, and distance of haul of 1.5 miles. Assume medium 


150 CONCRETE PRACTICE 


soil which will expand 20 per cent on excavation. Wage of unskilled labor is 
50 cts. per hr., foreman $1 per hr., man and team and 2-cu. yd. dump wagon 
is $1 per hr., driver and 214-cu. yd. auto truck is $3.50 per hr., operator 
and 34-cu. yd. steam shovel is $4 per hr. Estimator has choice of dump 
wagons or auto trucks. Allow 15 per cent for overhead expenses and 10 per 
cent for profit. Compute total costs and cost per cubic yard. 


Cost of General Excavation 


Assume output of steam shovel to be 1.50 cu. yd. per min. 


$4.00 
= SBGoscnl a Ga $0.0444. 


Time of haul for 1 team and wagon = loading 1 min., unloading 0.50 
min., time on road 90 min., totaling 91.50 min. per load. 
1.00 X 91.50 
1 GO alae $1.525. 

Cost per cubic yard = $1.525 + 1.5 = $1.0167. 

Time of haul for auto truck = loading 1.33 min., unloading 0.50 min., 
time on road (assuming 8 miles per hr. loaded and 15 miles per hr. empty) 
17.25 min., totaling 19.08 min. per load. 


Cost of digging per cu. yd. 


Cost per load at $1 per hr. = 


< 9. 
Cost per load at $3.50 per hr. = ae = $1.113. 
Cost per cubic yard = $1.113 + 2.0 = $0.5565. 
20,000 

Total time required for general excavation = 1.50 x 60 = 222.22 hr. 
Cost of foreman = $222.22. 
Cost of f bi d = at Sone 

ost of foreman per cubic yard = 55 Gog = 80. : 


Cost per cubic yard with trucks =$0 .6120. 

Use auto trucks. 

Cost of 20,000 cu. yd. = $12,240 + $1836 overhead + 10 per cent of 
($12,240 + $1836) profit = $15,484, or a cost of $0.774 per cu. yd. 


Cost of Special Excavation and Backfill 


For special excavation, assume labor output with shovel as 0.30 cu. yd. 
per hr. 


Cost per cubic yard at $0.50 per hr. = a8 = $1.667 per cu. yd., or $667 
for the job. 
Assuming eight men in shovel gang, time required will be ae = 


167 hr. 
Cost of foreman = $167 for job, or $0.418 per cu. yd. 


Cost of backfill, assuming 1.50 cu. yd. per man per hr., is a = $0.333 


per cu. yd., or $100 for the job. 
300 
aes Ram 


Cost of foreman for the backfill = $25 for job, or $0.0883 per cu. yd. 


Assuming eight men in gang, time required will be 


ESTIMATING 151 


Now there were 400 — 300 or 100 cu. yd. of special excavation to be hauled 
away. Using auto trucks, and assuming that this material is shoveled into 


the trucks as it is excavated, it will require or 50 min. to load a 


xX 6 
8 X 0.30 
truck with 2 cu. yd. Total time of auto truck for one round trip equals 
50 + 17.25 + 0.50 = 67.75 min. 


Cost per load = st SE = $2.3/1. 
Cost per cubic yard = zeae. = $1.186. 


Total cost of special excavation and backfill = $667 + $167 + $100 + 
$25 + $119 + $162 (overhead) + $124 (profit) = $1364 or a cost of 
$3.41 per cu. yd. based on 400 cu. yd. 

Total cost of general and special excavation and backfill = $15,484 + 
$1364 = $16,848 for the job. 

Cost per cubic yard based on 20,400 cu. yd. = $0.826. 


Ezxercises—Make an estimate of the cost of digging a basement 25 X 32 ft. 
and 6.5 ft. deep in medium soil, assuming 10 per cent to be special excava- 
tion. Use drag scrapers with an average haul of 65 ft. Assume wages of 
man and team at $1 per hr., and helper and shoveler at $0.50 per hr. No 
foreman on the job. Allow 15 per cent for overhead and 1214 per cent for 
profit. Compute total cost and cost per cubic yard. 

Make an estimate of the cost of digging and moving 35,000 cu. yd. of sandy 
loam using a 34-cu. yd. steam shovel, and 114-cu. yd. (net load) dump 
wagons. Length of haul averages 0.35 mile (0.70 mile for round trip). 
Assume capacity of shovel at 1.5 cu. yd. per min. (loading 1 wagon each 
minute) and cost at $4.50 per hr. Cost of man, team, and wagon is $1.10 
per hr. Assume foreman at $1 perhr. Allow 17 per cent for overhead and 
8 per cent for profit. Compute total cost of job and cost per cubic yard. 
How many: teams and wagons would be needed to keep the shovel working 
at assumed rate? 


JOB 42. ESTIMATING FORMS 


The unit of measurement for forms should be the actual area 
in square feet of the surface of the concrete in contact with the 
form. The estimated cost of the forms should include cost of 
struts, posts, bracing, bolts, wire, ties, oiling, cleaning, and 
repairing, but should not include cost of staging and bridging. 
Forms for each different part of the structure should be listed 
and described separately. Forms for moldings, window sills, 
and copings are measured by the lineal foot. No deductions in 
form measurement are made for openings having an area of less 
than 25 sq. ft., because the extra labor in forming around the 
openings will often cost more than the value of the lumber 
saved. No allowance is made for construction joints except in 
very large structures such as dams. 


152 CONCRETE PRACTICE 


Forms for How measured 
Floors h: ve in ee ee Total area in square feet. 
W alle Sic Sonas eee eee Total area in square feet. Forms may be 
placed on one or both sides. 
Columns) desc tptero ere: Circumference of the column in feet times the 


net height in feet from floor to floor. 
Column caps, drops, bands, | Total area in square feet. 
etc. 
ROOTS ic cos ate el Re Total area in square feet. When the slope of 
. the roof with the horizontal exceeds 25 deg , 
the upper side of the roof requires forms. 

Footings 3 fr cone eee Total area in square feet of concrete surface 
next to forms. 

Beams and girders.......... Total area in square feet. For a beam this is 
equal to the net length between columns or 
supports times the sum of the breadth and 
twice the depth. 

Staging and bridging........ No definite rules. Total number of thousand 
board feet required should be computed. 

Moldings and cornices...... Total number of lineal feet. . Other dimen- 
sions should be noted. 

Window sills, and copings... .| Total number of lineal feet. Other dimen- 
sions should be noted. 

Stair: Tek) oa oe en Total area in square feet, composed of area of 
the under side, areas of ends, and areas of 
risers. 


APPROXIMATE MATERIALS AND LABOR PER 100 Sq. Fr. or Forms, 
ASSEMBLING AND ERECTING 


Lumber, Nails or 

Kind of forms board bolts, Labor, hours 

feet pounds ; 

Footings and piers.....%....... 200-350 Way a a>) 5.0-11.0 
Walls and partitions, 2... .5... 200-270 1.0-1.4 8.0-14.0 
Ploors: 3.3+ a2 enone 180-280 0.7-1.2 4.0-12.0 
Roots 273.0 erea ee ae 200-300 0.8-1.3 4.5-14.0 
Golutons’. 32a 52 eee 190-320 0.7-1.4 6.0-12.0 
Column Gapsicsecs eee 200-400 0.8-1.4 8.0-18.0 
Beams and girders...........:. 300-700 0.9-1.6 9.0-14.0 
Stairs 22505, ah eee eae ee 300-600 1.0-1.6 10.0-20.0 
Molding and cornice!.......... 200-800 0.8-1.8 8.0-20.0 
Sills and jintele)s suas 250-800 0.8-1.6 7.5-16.0 


1 Per 100 lin. ft. 


ESTIMATING 153 


Staging and bridging should be estimated separately for each 
job, and no general values for this work can be given. 

Stripping and cleaning of forms will require from 2 to 5 hr. 
of time per 100 sq. ft. of forms. 

When the work permits re-use of forms of certain types, per- 
haps from 40 to 80 per cent of these forms may be re-used after 
repairs have been made. The amount of labor required for 
repair of forms varies greatly and may be estimated at from 2 to 
5 hr. per 100 sq. ft. of forms. The extra lumber for form repairs 
may vary from about 40 to 200 bd. ft. per 100 sq. ft. of forms. 

After old forms are repaired, they must be erected before use, 
and the labor of erecting will be from 25 to 50 per cent of the 
total time of assembling and erecting new forms. 

Form work is often all done by carpenters, but, when possible, 
a combination gang of carpenters, ‘‘handy men,” and ordinary 
laborers should be used to save expense. The proportion of the 
different classes of laboring men will vary in any gang, but one- 
third carpenters, one-third handy men or rough carpenters, 
and one-third laborers will not be far from the average. 

The cost of form lumber may vary from about $380 to $60 per 
thousand feet board measure, with average values of from $35 
to $50. 

The average cost of laborers will be about as follows: carpen- 
ters $0.80 to $1.50 per hr.; handy men or rough carpenters $0.50 
to $1 per hr.; and laborers from $0.40 to $0.60 per hr. 

Foremen will cost $1 to $2 per hr. and a good superintend- 
ent from $1.50 to $3 per hr. 

Overhead, labor insurance, etc. will vary from 10 to 20 per 
cent of the total cost, with 15 per cent as an average value. When 
based on labor costs alone, overhead costs will vary from 15 to 
AQ per cent. 

Profit on form work (when figured separately) will usually 
vary from 10 to 25 per cent. 

When there is no salvage value to the old form lumber, the 
total costs will usually be higher and the percentage of profit 
less. When some of the form lumber may be salvaged, it is 
often difficult to estimate this value, and the estimator may guess 
at a low salvage value and a low percentage of profit or vice 
versa. When forms are stripped, the salvage value of the old 


154 CONCRETE PRACTICE 


form lumber may be from 20 to 90 per cent of its original cost, 
depending upon care exercised by the stripper, and the possible 
use to which the old lumber is to be put. 

Nails and bolts will cost from about $0.04 to $0.06 per Ib. on 
the average, when purchased in quantity. 

Oil for oiling forms will cost a few cents per 100 sq. ft. of 
surface, say from $0.03 to $0.07, depending on kind and price of 
oil. 


Exercises.—Make a complete estimate of the form lumber required in 1000 
bd. ft., pounds of nails and bolts, labor in hours, and costs of each for the 
following form surfaces: foundations and footings 785 sq. ft.; walls 2180 
sq. ft.; columns, 3150 sq. ft.; column heads 1780 sq. ft.; floors 14,200 sq. ft.; 
beams 3160 sq. ft.; roofs 4100 sq. ft. Take unit prices as follows: Form 
lumber $38 per thousand board feet delivered at the job, bolts and nails 
$0.05 per lb., foreman $1.50 per hr., carpenters $1 per hr., handy men $0.75 
per hr., and laborers at $0.50 per hr. Assume that salvage value of form 
lumber will be 65 per cent. Allow 15 per cent of total cost for overhead and 
10 per cent for profit. Forms are to be made and erected and later stripped 
and cleaned. 


JOB 43. ESTIMATING CONCRETE 


In estimating concrete quantities, it is customary to use a 
sheet or page for each different mix, arranging columns on each 
page about in the following order: 

Description (footing, beam, etc.). 

Dimensions (of each unit in feet). 

Volume (cubic feet or cubic yards). 

Other columns may be added for unit and total prices, etc. 

In ‘‘taking off”? quantities of concrete it is customary to begin 
at the bottom or one end of the structure and go over it system- 
atically. In a concrete building, the order of ‘take off’? would 
be about as follows: 

Footings. 

Foundation walls. 

Columns (interior and exterior). (Ordinary column caps and 
brackets are usually included with columns.) 

Floor and roof slabs. 

Drop panels. 

Beams and girders (exterior and interior). 

Partitions. 

Window sills and copings. 


ESTIMATING 155 


Stairs. 

Sidewalks and drives. 

In general, all concrete is measured net, as fixed or placed in 
the structure. Units of measurement are cubic yards or cubic 
feet, cubic yards being the common unit. No deductions are 
made for steel beams and reinforcement in the concrete unless the 
steel has a cross-sectional area of more than 1 sq. ft. No deduc- 
tions are made for pipes or holes having a sectional area of less 
than 1 sq. ft. Each mix of concrete should be measured and 
described separately, and the concrete in different members of the 
structure should be measured and described separately according 
to location or purpose of the work. 

Many rules are given for measuring stairs, but the best rule is 
to compute the quantity of concrete required in cubic yards by 
some simple method. 

Sidewalks and pavements should be measured by the square 
foot or square yard with the thickness and mix stated. 

The unit of measurement for precast concrete work is usually 
the cubic foot. 

Curbs, gutters, window sills, lintels, moldings, and such work 
are often measured per lineal foot, other dimensions being given. 

Concrete finishing is measured by the square foot or square 
yard of finished surface. 

After the “take off’’ has been completed, and the total yardage 
for each mix totaled, the quantities of cement, fine and coarse 
aggregates should be computed by means of the formulas given 
in Job 12 for computing quantities of materials for concrete. 
The following table gives the quantities of material required for 
some of the common mixes: 


MATERIALS REQUIRED FOR 1 Cu. Yb. or CONCRETE 


Coarse aggregate, 
cubic yards 


Fine aggregate, 


Cement sacks arc eaeda 


Mix by volume 


i NR a 10.50 0.39 0.78 
1:114:3 7.64 0.425 0.85 
Lite. 4 6.00 0.445 0.89 
1:24%:5 4.94 0.46 0.915 
i Nar e e3) 4.67 0.52 0.865 
123295 °6 4.20 0.465 0.935 
1 Fee: lp e . 3.23 0.48 0.96 


156 CONCRETE PRACTICE 


To get cement in barrels, divide number of sacks by 4. 

The amount of water required will vary from 9 to 15 gal. per 
sack of cement, or from about 30 to 150 gal. per cu. yd. of con- 
crete, depending upon the water-cement ratio and the water used 
for washing mixer and equipment and wastage. About 100 gal. 
per cu. yd. of concrete is a good value for estimating purposes. 

The cost of materials delivered on the job is generally used, 
though on very large jobs the cost of cement will be the price at 
the mill plus costs of freight, unloading, trucking to job, storing, 
inspection and testing, and loss due to waste and spoiling. From 
the cost of cement in cloth sacks there should be deducted 10 cts. 
for each good cloth sack returned to the mill or dealer. As a 
general rule, about 10 per cent of the cloth sacks will be wasted. 
When the cement comes in bulk or in paper sacks, there will, of 
course, be no credit for returned sacks. Quotations of prices 
usually given by cement companies are for the cost of cement 
f. o. b. cars at the station near which the job is located. To this 
price must be added the cost of testing, unloading, and trucking. 
Average cost of cement (without sacks) will be from $2 to $3 per 
bbl. for large quantities, or $0.50 to $0.75 per sack. 

Assuming $0.65 per sack, or $2.60 per bbl., the cost of cement 
at the job will be about as follows: 


Cost oF CEMENT 


Item | Per sack | Per barrel 

Cement i. 0.:D) Carer te fess Se ee $0.65 $2.60 
Gotton sacks: 67. si2. hens ea 0.10 0.40 
Resting t)..20)idicnyd ae See ee eae 0.01 0.04 
Unloading, trucking, and storing about......... 0.05 0.20 

Total) é.c.a8 | overeating As i $0.81 $3.24 
Credit for sacks returned less loss and freight... . . 0.09 0.36 
Net: cost of. cement at jobeds &.. 2. 0i te. ee $0.72 $2.88 


The cost of sand, gravel, and crushed rock at the job will vary 
greatly in different localities. The following are approximate 
prices only, and for relatively large quantities: 


ESTIMATING 157 


Cost or AGGREGATE 


. Weight Per | price sey oa Price per 
Material cubic yard, cubic yard, 
dollars 
pounds dollars 
CEL adits 2700 1.10-2.50 1.50-3.40 
oe gs Pacts eee or 2700 1.50-2.50 2.00-3.40 
Crushed stone.............. 2500 1.80-3.00 2.25-3.75 


The cost of water can best be found by finding the local rate 
per 1000 gal. and multiplying this rate by the number of thousand 
gallons required. In most localities there are also extra charges 
for setting the water meter and turning the water on and off. 

The amount of labor hours required to mix and place a cubic 
yard of concrete varies greatly according to the nature of the job 
and conditions of the work, kind of plant, and skill and inclination 
of the workers. 

The following are approximate values: 


Laspor REQUIRED TO Mrx AND PLACE CONCRETE 


Labor per cubic yard 


Kind of work of concrete in 

hours 
Gs a, Sw yo sb are cs we as wae es 3 to 6 
ROTM CLINGS o.oo. ba ox le kee ee 4to7 
COLES ADEN 0 A ene 2 to 5 
Thin floors and pavements less than 5 in. thick .... 3 to 6 
Thick floors and pavements more than 5 in. thick. . 2 to 5 
RAG <a Ge nr a 4to8 


If the mixing is done by hand, from 1 to 2 labor hr. per cu. yd. 
of concrete must be added. | 

With the foreman at $1 to $2 per hr., mixer operator and other 
skilled labor $0.75 to $1.50 per hr., and ordinary labor at $0.50 
to $1 per hr., the average cost of labor for mixing and placing 1 
cu. yd. of concrete will vary from about $1.75 to $4.50. 

The plant cost of mixing and placing 1 cu. yd. of concrete will 
vary considerably, depending upon the kind and conditions of the 
work, arrangement of the plant, amount of plant, and efficiency of 


158 CONCRETE PRACTICE 


plant operation. In general, a large plant will result in less labor 
per cubic yard of concrete, and vice versa. 

Plant costs per cubic yard of concrete at present writing will 
vary from about $1.25 to $3 per cu. yd. In general, the unit 
plant costs on large jobs, say from 8000 cu. yd. or over, are less 
than those on smaller jobs ranging from 2000 to 6000 cu. yd., 
other things being equal. An elaborate complete plant will tend 
to cost more per cubic yard of concrete than a simple plant will, 
but the saving on labor costs may more than offset the extra 
plant costs. 

Plant costs include not only the mixer costs, but also the costs 
of barrows, shovels, and concreting tools, carts, hoists, towers, 
bins, buckets, chutes, runways, etc. Mixer costs alone may vary 
from about $0.40 to $1.25 per cu. yd. 

Overhead charges on mixing and placing concrete work may 
include cost of labor and other insurance, superintendent, time- 
keeper, night watchman, general office expenses, telephones, 
stationery, sundries, etc. Cost of foreman is usually included in 
labor costs. 

Exercises.—Compute total cost of materials, and the mixing and placing 


of 1650 cu. yd. of concrete, assuming the following: 
Mix is 1:2:4 by volume: 


Cost of cement per sack at Joba: 222). ee = $078 

Cost of sand per cubic yard at job.... ... sae = $2.10 

Cost of crushed rock per cubic yard at job........ = $2.45 

Cost of water per 1000 gal; .:2... 04.3 oe = $0.10 

Cost of plant per cubic yard of concrete.......... = $1.90 
Labor hours per cubic yard of concrete........... = 4,50 hr. 
Average cost of labor per hour in concrete gang.... = $0.80 
Overhead expense, .. 0... 2. ees on os oe ee = 16 per cent 
Profit. 25. wii s cam aielaate <a ee = 10 per cent 


Also compute the cost of each item and the total cost per cubic yard of 
ecncrete. 


JOB 44. ESTIMATING STEEL FOR REINFORCEMENT 


Steel for reinforcement should be estimated in pounds, assum- 
ing that a square bar 1 X 1 X 12 in. long weighs 3.4 lb. In the 
“take off,” reinforcing bars should be listed with reference as to 
whether they are plain bars, deformed bars, spirals, round or 
square bars of different diameters, bent bars, or straight bars, 


ESTIMATING 159 


and also with reference to the places where they are to be used. 
Chairs, ties, pipe sleeves, clamps, units, threaded ends, turn 
buckles, etc. should be tabulated separately. Wire cloth, 
expanded metal, and similar steel fabric sold by the roll or sheet 
should be measured and described by the square foot, stating size 
of mesh and weight per square foot. Allowances should be 
made for waste, cutting, laps, etc. 

The ‘‘take off” sheet for reinforcing steel should have columns 
for size of bar, number of pieces, length, and bends. The sum- 
mary sheet should give size of bar, weight per lineal foot, total 
weight, bends, unit price, and total price. Separate sheets 
should be prepared for plain and deformed bars, spirals, stirrups, 
and for accessories, such as chairs, ties, clamps, ete. 


WEIGHTS OF Bars IN PounpbDs PER Foot or LENGTH 


Pe aaaed Round Square pacers Round Square 
inches inches 

yy 0.17 0.21 1% 3.38 4.30 

34 0.38 0.48 1% 4.17 5.31 

12 0.67 0.85 138 5.05 6.43 

58 1.04 1.33 11g 6.01 7.65 

34 1.50 191 15g 7.05 t 492908 

1% 2.04 2.60 134 8.18 10.41 

1 2.67 3.40 2 10.68 13.60 


Unit base prices of reinforcing steel vary at the time of writing 
from about $3 to $4 per 100 Ib. for bars of 34 in. in diameter, and 
larger. Bars of smaller diameter, or of a length less than 5 ft., 
are a little higher in price. Small special discounts are often 
given for ton lots or more. Deformed bars cost a little more than 
plain bars. 

Extra Prices on Stee, REINFORCEMENT Bars 
Per 100 lb. or fraction thereof, according to size 


Uy 1a esa a Base + $0.20 


Size, inches Price | Size Price 
34 and larger..... Base 3¢ Base + $0.25 
32 to 1ig.......- Base + $0.05 546 Base + $0.35 
Uh Base + $0.10 yy Base + $0.50 


160 CONCRETE PRACTICE 


ExTRA PRICES ON STEEL REINFORCEMENT Bars 
Per 100 lb. or fraction thereof, according to length 


Length Extra price 
BELO OR OVET iG cca oe ee None 
Over 4 ft. and less than Sft.. >>... <...+,5 +s $0 .05 
2 to 4 ft., Inclusive... so 5. ca oe $0.10 
1 ft.to 1 ft. 11 in,, inclusive ...¢ 0.7.) Se 2 $0. 20 
Under 1:ft.,; not less:than,.. ..4.<). 4,5 +. 2) bones eee $0.30 


Steel bars in other than 1¢-in. sizes are rarely kept in stock by 
most dealers, hence the estimator and designer should not use 
14 ,6-in. sizes. 7 


Time In Hours REeQuirED FoR Maxine 100 E1cHTH or QUARTER BENDS 


Diameter of bar, Hand bending, Machine bending, 
inches hours - hours 
te -OVNOSS. “dia pe Eee 2.00—4.00 0.75-1.50 
34 ANGRS iy cee eee 2.50—-5.00 1.00—2.00 
Vesind [1Jeec. ay eee ae 3.25-6.00 1.25-2.50 
14 iand 144 a Aw aes 4.00-7 .00 1.50-3 .00 


TimE IN Hours REQUIRED FOR PLaciInG 100 Bars 


Length of bar 
Diameter of bar, inches Under 10 ft. | 10 to 20 ft. | 20 to 30 ft. 


Time required in hours 


+4 .0Y lees ce ae eee 3.5-6.0 5.0—- 7.0 6.0- 8.0 
24 ONG Geo ae cart Eee ae 4.5-7.0 6.0— 8.5 1.0 9:5 
Lean iid ie ee ee ee 5.5-8.0 7.0-10.0 8.5-11.5 
T34 and 156 ee Bas ee eee 6.5-9.0 8.0-12.0 10.0-14.0 


The bending and placing of steel reinforcement bars may be 
done by handy men at an hourly wage of from $0.50 to $1, under 
the direction of a competent foreman (wage $1 to $2 per hr.). In 


ESTIMATING 161 


localities where union rules require a certain class of laborers, the 
wages of the laborers will probably be from $1 to $1.50 per hr. 

In regard to chairs, spacers, ties, etc., the total cost of these 
will vary greatly, depending on the kind used and the number 
required. An allowance of from $0.15 to $0.50 per 100 lb. of 
reinforcing bars is usually satisfactory. 


Exercises—Compute the weights and costs of the following reinforcing 
steel, using a base price of $3.65 per 100 Ib. Allow 35 cts. per 100 lb. for 
chairs and ties. 


Lineal feet Number of bars 
bize, ck rods 0-10 | 10-20] 20-30 | B°?28} 6-10 | 10-20 | 20-30 

it: ie at fie ft. tt: 

Sen etTOUnd) es... 106 612 | 274 | None} 14 44 16 

Peinei fount. ......1 318 948 0 86 42 66 0 

34 in. (round)......... 462 | 894] 316| 56 | 57 | 52 | 28 

Mean (round) ..:.....| 746.| 1264 836 12 96 74 38 
41g in. (square)....:... ere ISOs) ware 12 e 14 
ATC ECIIASE) 6 ob os ccs 5 ee 192 8 Me 12 


3g in. (round) for spirals} ... ... | 2856 | None 


Compute the cost of bending and placing the steel, in the previous ques- 
‘tion, assuming that all work is done by a gang of three handy men and a 
foreman. Foreman’s wage is $1.50 per hr., and wage of handy men is 
$0.85 per hr. The 2856 ft. of 3g-in. round bars for spirals will be assumed to 
be in 86 units, all bent in spiral form ready to be placed in column forms. 
No labor allowance need be made for placing the spirals in the column forms 
and tying them to the column rods, as this labor is included in the labor 
estimate for placing column rods. Allow 18 per cent for overhead. 

Compute the total cost of the steel of the previous two exercises all placed 
in forms. Allow 11 per cent for profit. Compute cost of steel per 100 lb. 
and per ton (of 2000 lb.) in forms. 


JOB 45. ESTIMATING FINISHING OF CONCRETE SURFACES 


The cost of finishing concrete surfaces varies according tothe 
price and quantity of materials used, kind of finish desired, labor 
hours required, labor wage per hour, and speed at which the men 
work. 

The following values are approximate and will vary greatly in 
different localities: 


162 CONCRETE PRACTICE 


Labor, Cost, 
mons hours dollars 
Troweling floors, walls, sidewalks, etc. (100 sq. 

TO. ite Bato ee ee ees et i ae ee 2- 5 1.50— 5.00 
Troweling plain base, cove, etc. (100 lin. ft.)..... 2-5 1.50— 5.00, 
Troweling fancy base, cove, etc. (100 lin. ft.).... 3— 6 2.00— 6.00 
Carborundum rubbing of floor and wall surfaces 

(LOO eqs Ete tae kee Saleh Soe eee ene ene 4-10 3.00—-10.00 
Carborundum rubbing of window sills, base, 

cove, ete-(L00 Lins ft.) ccs 0: aya perenne 4-10 3.00-10.00 
Ornamental tooling (100 sq. ft:)......4..:.0.5- 8-16 6.00-15.00 


1in. granolithic finish laid after concrete has 

hardened, including materials and labor (100 

BQ ATO ais Clateae. Ws ce ae ene 7-12 7.00-14.00 
1 in. granolithic finish laid integral with the con- 

crete, including materials and labor (100 sq. 


Tb) Sc ase BOE re alee es scala ag ea ee 4-8 5.00— 8.00 
Scrubbing surface: 100/sq. it.) vans eee eee 2- 5 1.50— 4.00 
Washing surface with acid (100 sq. ft.)......... 2- 5 1.50— 4.00 
sand. blasting surface -(100 sq.ift,)s.... 3) eee 3— 5 2.25— 5.00 
Cement surface wash per coat including materials 

(TOO WSC 1t..):,.c eas Woe es ceca eae 2- 5 2.50— 5.00 


A 1-in. granolithic finish will require, per 100 sq. ft. of surface 
area, 1 to 1.25 bbl. of cement, and from 700 to 1000 lb. (about 7 
to 10 cu. ft.) of aggregate. The aggregate may be part sand and 
part fine-crushed stone, or all fine-crushed stone with no sand. 

In concrete finish work, from 12 to 20 per cent must be added 
for various overhead expense. 


Exercises.—Estimate cost of finishing 1275 sq. ft. of surface by the fol- 
lowing methods: 


Labor hours 
Method per 10084 te Hourly wage 
Carborundum rubbing ABA etn Ro 6.20 $0.85 
Omamentalstoolinge ene oe oe 10.50 $0.95 
Washing with seid oe .e. 4 ee 3.40 $0.90 


Allow 16.5 per cent for overhead and assume this figure to cover cost of 
materials. 


ESTIMATING 163 


JOB 46. ESTIMATING MISCELLANEOUS ITEMS 


In the average concrete structure, there are frequently many 
items other than the excavation and the concrete work. Many 
of these items are given in the paragraphs which follow, together 
with their estimated costs. These cost estimates are approxi- 
mate only, and will vary greatly due to locality, material, wages, 
and efficiency of laborers. 

The approximate cost of brick work in place varies from about 
$30 to $75 per thousand brick. This includes cost of brick, 
mortar, labor, and scaffolding. Costs of laying vary from about 
$20 to $40 per thousand. In order to estimate the approximate 
number of brick, the following table is suitable for standard size 
brick (214 X 3% X 8 in.) laid with !4-in. joints: 


Estimated number of 
Thickness of wall brick per square foot 
of wall surface 


ae) 40.—1 standard brick width................. 7 
$ in:—2 standard brick width................. 14 
12% in.—3 standard brick width................. 21 
17 in.—4 standard brick width................. 28 


When estimating the number of brick, deductions for window 
and door openings are made only for about 50 per cent of their 
area, due to wastage of brick in cutting and fitting them around 
the openings. In estimating the labor, no deductions are made 
because of the extra labor in cutting, fitting, and laying the brick 
around these openings. The labor of laying a thousand of brick 
decreases with the thickness of the wall. 

Terra cotta partitions will vary in cost from $20 to $30 per 
100 sq. ft. of wall surface. 

Concrete block masonry will cost from $45 to $75 per 100 block 
in the wall, assuming total labor and mortar costs of laying 100° 
blocks to vary from $8 to $15, and the blocks to cost from $35 to 
$60 per 100 delivered at the job. The average size of a block in 
the wall is about 16 in. long X 8 in. wide X 8 in. high. The 


164 CONCRETE PRACTICE 


number of blocks of this size per 100 sq. ft. of wall surface will be 
about 115 (allowing a few for wastage) for an 8-in. wall. 

The cost of plastering will vary to some extent on the cost of 
materials, labor wages, and labor efficiency. On many jobs, the 
lathing and plastering are let as subcontracts. 


Item Cost per 100 sq. yd. 
Wood: lath in: place, 225) ois os ae $15 to $30 
Metal lath ‘mn place i4.. 0%. 334 ee 20 to 40 
Two-coat. plaster m placest.i.:.2) 4 Aas ) eee 30 to 60 
Three-coat plaster*m place....... ...2. se eee 40 to 75 


Hence the total cost of a two-coat plaster job on wood lath 
would vary from $45 to $90 per 100 sq. yd. 

Steel sash without glass cost from $30 to $50 per 100 sq. ft. of 
opening. 

Wood sash without glass cost from $15 to $30 per 100 sq. ft. of 
opening. With glass, the cost is $385 to $65 per 100 sq. ft. of 
opening. 

Glass and glazing cost from $20 to $35 per 100 sq. ft. Glass 
area 1s often assumed as 90 per cent of sash area. 

The cost of a single door and frame in place, complete with 
hardware, will vary from about $20 to $60. A pair of French 
doors with frame and hardware in place will cost from $75 to 
$125. 

Baseboards, molds, and other wood trim in place cost from $15 
to $30 per 100 lin. ft. 

Tongue and grooved flooring in place will cost from about $18 
to $30 per 100 sq. ft. of floor area. Rough flooring 1 in. thick 
will cost about half as much. 

No general estimate of cost can be made for light iron work 
and miscellaneous iron work. 

Flashing may be estimated at from $30 to $100 per 100 lin. ft. 
depending on kind and weight of material, copper flashing being 
the most expensive. 

Metal roofing in place will cost from $15 to $25 per sq. of 100 
sq. ft. of roof surface for iron or tin, and about three times as 


ESTIMATING 165 


much for copper. All metal flashing and roofing is usually let as 
a subcontract. 

A composition roof (tar and paper) covered with gravel will 
cost from $10 to $20 per 100 sq. ft. of roof surface. 

The cost of good composition shingles in place will vary from 
about $15 to $30 per 100 sq. ft. of roof surface. 

The cost of good wood shingles in place will cost from about 
$12 to $30 per 100 sq. ft. of roof surface. 

Cost of stucco per 100 sq. yd. varies greatly with the materials 
used, number of coats, thicknesses of coats, wood or metal lath, 
wages, and efficiency of labor. The cost of lath and stucco in 
place may vary from $50 to $125 per 100 sq. yd. 

The cost of painting varies greatly in regard to quality of 
paint, kind of surface to be covered, number of coats, wages, and 
efficiency of workmen. Average prices are from $1.50 to $3 per 
100 sq. ft. for one coat. ‘Two-coat work will cost from $2.75 to 
$5.50 per 100 sq. ft. 

Cleaning up the job costs from about 149 of 1 per cent to 14 of 
1 per cent of the total cost. 

Plans and specifications cost from 21% to 3 per cent of the total 
cost. 

Cost of inspection varies from 2 to 3 per cent of the total cost. 

Liability insurance varies from 5 to 10 per cent of the labor 
cost. 

Sundries vary from about 2 to 5 per cent of the total cost. 

General overhead expenses including office expenses, traveling 
expenses, job overhead superintendence, timekeeper, office clerks 
and stenographers, draftsmen, watchmen, telephones, freight, 
stationery, interest, insurance, etc., may vary from 10 to 20 
per cent of total cost. 

Profit is usually estimated at from 8 to 15 per cent depending 
on the conditions governing the particular job. 

Such items as lathing and plastering, metal roofing and flashing 
and other metal work, heating, plumbing, lighting, painting, etc. 
are frequently let as subcontracts. Plumbing fixtures cost from 
$60 to $100 per fixture, heating from $75 to $125 per radiator for 
steam and hot-water heat, and from $50 to $75 per hot air register 
for hot air heat, lighting from about $5 to $12 per drop or light 
outlet with fixtures extra. 


166 CONCRETE PRACTICE 


Summarizing, the items of cost of a concrete structure to the 
owner may be listed as follows. 

Architect’s fees and commission. 

Main contract, including excavation, forms, concrete, steel, 
finish, cleaning up, sundries, overhead, and profit. 

Subcontracts—if let separately. 

Extras. 

Land, including proving of title, etc. 

Interest and insurance during construction. 

Cost of financing. 

Profit to owner, if he sells. 


Exercises.—On what items does the cost of brick work depend? 

What items are usually let as subcontracts in concrete building construc- 
tion? 

Which wall would be cheaper: an 8-in. brick wall with brick costing $28 
per thousand and complete labor and mortar costs of laying brick in wall of 
$34 per thousand, or an 8-in. concrete block wall made with blocks about 8 X 
8 X 16 in. in size and costing 45 cts. each on the job, and complete labor and 
mortar costs of laying block in the wall of $12 per 100 blocks? 


JOB 47. SQUARE AND CUBE METHODS OF ESTIMATING BUILDING 
COSTS 


While the only safe and sure means of estimating is to take off 
actual quantities of materials and hours of labor, and use the 
local unit prices prevailing in order to determine the total cost of 
the structure, many experienced estimators use the approximate 
methods of estimating certain types of structures by the cube or 
square, in order to obtain approximate costs in a short time, and 
also as a comparison and rough check on the costs found by the 
more accurate methods. 

The method of estimating by the square of 100 sq. ft. or 1 sq. 
ft. of floor area is applicable to office buildings, schools, mills, 
warehouses, factories, hospitals, churches, stores, residences, 
and garages. This method is useful in comparing the costs of 
different buildings, where the floor area is important, as in offices 
and factories, and in determining the capacities and costs per 
person, as in schools, churches, and hospitals. 

There are several variations in estimating buildings by the 
square. One method is to allow a certain figure per square foot 
for each floor, and use other figures for the roof and foundation 


ESTIMATING 167 


areas. Another method is to use different unit prices for the 
different floors—the lower floor to include cost of foundations, 
and the upper floor to include cost of roof. A third method is to 
use the same unit price per square foot of floor area for all floors, 
omitting the roof area or both the roof and basement areas. 

The method of estimating building costs by the cube or volume 
is more accurate, in general, than the method of estimating by 
the square. The best method of estimating by the cube is to 
find the total volume of the building in cubic feet, and multiply 
this volume by a selected unit price per cubic foot for this particu- 
lar class of building. Another method is to use a certain unit 
cost per cubic foot for the part of the building that is more 
expensively finished, and another price for the portions that are 
more cheaply or less completely finished. For example, in a 
residence, the cubic contents of the basement, attic, and garage 
would have one unit price, and the living-room, dining-room, 
kitchen, halls, bath, and bedrooms would have another unit 
price. A third method is to consider only half or two-thirds of 
the volume of the basement, attic, and garage, when computing 
the cubic contents of a residence, and then use the same price per 
cubic foot for all parts of the building. Of course, buildings of 
different types and kinds of construction would require different 
unit prices per cubic foot. | 

Exerctses.—A certain building is 40 X 60 ft. in size and consists of base- 
ment, first, second, and third floors, and attic. Assume heights (including 
floor thickness) of 8.5, 10, 9, and 9 ft. for basement and the first, second, and 
third floors, respectively, and an average height of 7.5 ft. for the attic. Cost 
of building was $44,270. 

Compute the cost per square foot by each of the following methods: 

1. Based on the floor area of the three floors. 

2. Based on total area of three floors, basement, and roof, assuming roof 
area equal to one floor area. . 

3. Based on area of three floors and basement. 

4. Based on area of three floors, assuming that the cost of the first floor 
is 1.60 times the cost of the second, and that the cost of the third floor is 
1.50 times the cost of the second. 

Compute the cost per cubic foot by each of the following methods: 

5. Based on the total volume of the building in cubic feet. 

6. Allowing full value for the three stories, 60 per cent of the value for the 
basement, and 50 per cent of the value for the attic. 


Note.—Take cubic feet for the three stories, and add 60 per cent of the 
cubic feet in the basement and 50 per cent of the cubic feet in the attic. 


168 te CONCRETE PRACTICE 


JOB 48. SAMPLE QUANTITY ESTIMATE FOR CONCRETE WORK 


In this job, a sample quantity estimate will be made of the 
materials and labor required for the reinforced concrete slab 
shown in Fig. 71, page 140. It will be assumed that the estimates 
have been previously prepared for the abutments. 

The estimate will be divided into four parts: forms, steel, 
concrete, and surface finish. A “‘take off” of the quantities will 
be made first, and then an estimate of the labor will be given. 
It is to be remembered, that all labor estimates are approximate 
only. 

Forms. 

Under side of floor slab = 30 X 16 = 480 sq. ft. 

Ends of floor slab (allowing for pavement notch) 

= 2 30 X 15 = 75 sq-it: 

Sides of floor slab = 2 X 16 X 2 = 64 gq. ft. 

Railings, two rails, sides and ends 
=(2X2xX3xX19 +2X2xX 3X DiS 

| 240 sq. ft. 
Total square feet of form surface 
= 480 + 75 + 64 + 240 = 859 sq. ft. 

In determining the number of board feet required per 100 sq. 
ft. of form surface, it should be noted that the form lumber must 
be of selected lumber carefully fitted together and rigidly braced. 
This means that there will be considerable wastage even under 
the most favorable conditions. The shoring for the slab, and 
the paneling of the railing will require considerable lumber. An 
allowance of 525 bd. ft. of lumber will be made for each 100 sq. 
ft. of form surface for this estimate. This can be checked, when 
a bill of materials is made for the form lumber. 


525 & 859 
"0. ae 4500 bd. ft. of 


lumber. ah} 

Allowing 1.5 lb. of nails and bolts per 100 sq. ft. of form surface 
gives 1.5 X 8.59 = 13 lb. nails and bolts. 

The hours of labor required per 100 sq. ft. of form surface will 
be comparatively large, due to the care with which the forming 
must be done. For this estimate, 12.5 labor hr. per 100 sq. ft. 
of forms will be assumed for assembling and erecting, and 3.5 


Total lumber for forms will be 


ESTIMATING 169 


labor hr. per 100 sq. ft. of form surface for stripping and cleaning 
forms. Labor hours for forms = | 
(12.5 + 3.5) X 85999 = 187.5 labor hr. 
Concrete Materials——The number of cubic yards of concrete 
required is given in Fig. 71 as 27.5 cu. yd. A check will be made 
of this quantity as follows: 


Floor slab sae or OU x 1125 =O UHLCUS LL 
Rails eee 11) XU. ooo 15.0 4 L115 cu, ft. 
Curb eee 0.70) U.00ExX 18.0, = 14 eu: it: 
Total 754 cu. ft. 
Deduction for pavement notch 

Bee o8T x 1 xX 0.88 = is CU site 
Net concrete PAOCCUL al Gee = 

27.3 cu. yd. 


There is no allowance here for wastage or possible slight over- 
run. Will use 27.5 cu. yd. in estimating materials, and add about 
5 per cent for wastage. 

Materials required for 27.5 cu. yd. of Class A concrete of 1:2:4 
mix, are: 

Sacks of cement 


27.5 X 42 
es 4 = 165 sacks, assume 168 
Cubic yards of sand 
pee el DOT 2 
= "eg a 12.2 cu. yd., assume 13 


Cubic yards of stone or gravel 
Beat.0 XX 1.00-x< 4 
— j1+2+4+4 

The water required will be approximately 2750 gal. 

The values assumed allow for about 5 per cent wastage. The 
wastage of aggregates will usually be a little more than that of 
cement. 

The labor hours required to mix and place concrete in a bridge 
will be comparatively high, possibly from 4 to 7 hr. per cu. yd. of 
concrete. The roadway surface must be finished as it is laid. 


= 24.4 cu. yd., assume 26 


170 CONCRETE PRACTICE 


For this job, 5.5 hr. of labor per cu. yd. of concrete will be 
assumed. ‘Total labor hours required for mixing and ee 
concrete will be 5.5 X 27.5, or 151 hr. 

Consideration of the concrete plant will be made in the cost 
estimate. The plant and crew must be large enough, so that all 
of the concrete for the slab bridge, except railings, can be placed 
inl day. <A 2- or 3-bag (14 to 4 cu. yd.) batch mixer would do. 
The mixer will be used about 2 days. 

Reinforcing Steel. The Bill of Bars given in Fig. 71 may be 
taken as correct, and the total weight checked. 


Num- Me Bina Length, ae Weight per Total 
ber feet f foot, pounds | weight 
eet 

33 S1 | 7é-in. round bars} 18.00 | 594 2 O44 ag 
32 S2 | 7%-in. round bars| 18.25 585 2.04 1193 
26 S38 | %-in. square bars 4.75 124 0.85 105 
10 S4 | -in. square bars} 18.00 | 180 0.85 153 
17 S5 | -in. square bars} 29.75 | 506 0.85 430 
Total — 

weight 3093 Ib. 


For chairs, spacers, and ties for bars assume about 125 lb 
The number of bends is as follows: 


Mark Size Number of bends 
DLs Ruaes oes sca ey 7g-in. round bars 132 
PP te SS i ae 7g-in. round bars 64 
BBL se saves Lees ee J4-in. square bars 26 
Total. ess Boe ce ell 2) a ee ee 222 


Labor in hours required for bending steel, assuming hand bend- 
ing, will be about 3.5 hr. per 100 bends, giving a total of 3.5 X 
222/99, or about 8 hr. | 

The labor of placing the bars may be estimated as follows: 


ESTIMATING 171 


65 Sl and S82 7%-in. round bars at 7 hr. per 100 = 4.55 hr. 
26 S3 14-in. square bars at 6 hr. per 100 = 1.55 hr. 
10 S4 1g-in. square bars at 6 hr. per 100 = 0.60 hr. 
17 S5 1g-in. square bars at 6 hr. per 100 = 1.00 hr. 
motels: <. (egiaite 
(say 8 hr.) 


Surface Finishing.—The specifications require a two-coat 
carborundum rub on the surface of the bridge rails and on the 
exposed sides of the slab. Total area to be rubbed is approxi- 
mately as follows: 


Rails = 8 X 19.5 X 4 = 624 sq. ft. 
Sides = 2 X 2 X 16 = 64 sq. ft. 
(one 688 sq. ft. 


Assuming 7 hr. labor per 100 sq. ft. of surface for the first rub 
coat, and 5 hr. labor per 100 sq. ft. of surface for the second rub 
coat, the total labor hours for carborundum rubbing will be 
(7 + 5) X 888490 = 82.5 hr. 

The upper surfaces of the slab floor and curb were finished 
when the concrete was placed. Removing fins, smoothing sur- 
faces, etc. on the under side of the bridge would require about 12 
hr. labor for approximately 500 sq. ft. of surface area. 


SUMMARY OF ESTIMATE 


Item Materials Labor 
[is 9) YS AO are 4500 bd. ft. lumber, 13 lb. nails and bolts. ..| 137.5 hr. 
Concrete........ TGS BACKS CRINGH Greer, osu oa. Le tae 1 Coeur 


13 cu. yd. sand 
26 cu. yd. stone 
2750 gal. water 


Ae es an SUES heel ef es Pate ae, eRe Cen Riernee iad Same Sanam neue 16h. 
125 lb. spacers, ties, etc. 
FAGSHING 0 7... GSS Bite GAT DOTUDOUT foc.) Rs eee Ome 94.5 hr. 


500 sq. ft. rough 


L722 CONCRETE PRACTICE | 


JOB 49. SAMPLE COST ESTIMATE FOR CONCRETE WORK 


A cost estimate will be prepared for the reinforced concrete 
slab bridge of Fig. 71, for which the materials and labor were 
estimated in the previous job. Assume that the bridge is located 
about 3 miles from the source of supply of materials, and that 
there is a good concrete road from the source of supply to the 
bridge site. All materials will be purchased from local dealers 
and delivered at the bridge site. Estimates are to nearest $1. 


Cost ESTIMATE 


Materials..2.4500: bd. ft eens at $42 per thousand 
For less. salvage: c+ ’.-csde meee ene at $15 per thousand = $122 
race 13 Ib. nails and bolts.......... ik 
Tabor een 137 {D2 htayo.ts een tee at $0.65 per hr. = 90 
Total for forms. iii 0 05 008 acess ote me clon ene eae nee $213 
Materials. 42.3093 1b: Darses ee eee at $0.0365 per lb. = $113 
Steel...... 125 lb. spacers and ties........ at $0.08 per lb. = 10 
abort AG. BAT chore ore yon gle ae er at $0.60 per hr. = 10 
Total for steel. .'.6 osc occ 0 0.0.5. 0.005 ass einertelico te, = eee arene ae aoe $133 
( Materials. ...168 sacks of cement........... at $0.67 per sack = $113 
13°eu.-yG.1sand? > eee at $1.95 per cu. yd. = 25 
ee i peg 26 cuceyd. stone, 400.) eee at $2.20 per cu. yd. = 57 
Wateriina. 2s cee ee eee 5 
Tabor LS] chr 8s wae ee at $0.60 per hr. = 91 
Plant estimated .9..06c% <6. s0ls 6 50:0 0 nite ae Paeue eee ane ae 40 
Total for concrete. 0.0.6.5 ies 3 oo 2 eee $331 
Mnighing labor... ..ece ee O4 DATS ann Giese eee at $0.60 per hr. = $57 
Superintendence and overhead....5 <6. oc ose «sew o> oo ones eee iene na anne ae een eee $125 
Profitea cc ci scaw oie 6 ceo. cb 0 6/8 6 oa ube Hiv leks’ ows eee Yen as a) eee oneal See ene een an $110 
Total bid oo 0es eo nc ed ne ewe ola tuna a cle e Eels a $996 
Cost per cubic yard, 2755 cu. yds. 6 oak ues vic oo eines oie ee $ 36.50 


Exercises —What would the total cost estimate for the reinforced concrete 
slab bridge have been if: 

Lumber cost $39 per thousand with a salvage value of $12 per thousand 

Steel cost $0.0352 per lb. delivered on the job. 

Cement cost $2.75 per bbl. delivered on the job. 

Sand cost $2.05 per cu. yd. delivered on the job. 

Good gravel cost $1.90 per cu. yd. delivered on the job. 

Overhead and superintendence cost 17 per cent. 

Profit is estimated at 10 per cent. 

Other prices the same. 

Also compute cost of concrete per cubic yard in the completed job. 


ESTIMATING 173 


JOB 50. TIME AND WORK SCHEDULES FOR CONCRETE JOBS 


On medium-sized and large concrete jobs, it is advisable to 
provide time and work schedules for the convenience of the main 
office, superintendent, and foremen. Such a schedule notes the 
different construction operations, the estimated dates that each 
operation should start and finish, and the actual dates. Such a 
schedule, together with progress reports and charts (if the job is 
a large one), enables the contractor or engineer to note if the work 
is progressing as planned, and to observe which items are ahead 
or behind the schedule. 

Certain construction operations and trades should follow each 
other in regular order and without interference. Confusion, 
with a resulting loss of efficient work, often occurs, when two 
comparatively large gangs are scheduled to work on the same part 
of ajob at the same time. Two small gangs may frequently work 
on the job at the same time (such as plumbers and electricians 
doing rough plumbing and wiring in a residence), without inter- 
ference. In general, the paint gang should come last (except for 
priming coat work) on any section of the job, and after the other 
gangs have completed their work. 

It is not necessary for any one operation to be wholly com- 
pleted before another operation is started, but the work should be 
so planned that the different operations do not interfere with 
each other. For instance, on concrete paving work, the excava- 
tion gang should be about a half a day or so in advance of the 
roller, and the concreting gang should follow about a day behind 
the roller. This allows the work to go forward efficiently, pre- 
vents interference between gangs, and permits the general 
superintendent or contractor to speed up any gang that is lagging. 

In order to note if the work is progressing according to schedule 
it is usually required that the superintendent, general foreman, 
inspectors, or timekeepers (depending on to whom the duty is 
assigned) make a daily report or record of the different kinds and 
quantities of work done. In addition to making the daily reports 
or records, a daily diary should be kept by the proper official in 
which all essentials relating to the particular job are noted. In 
general, the superintendent or general foreman is the best person 
for preparing and signing the daily reports. 


174 CONCRETE PRACTICE 


The following schedule is for the work on a garage building: 


TIME AND WorRK SCHEDULE 


Type of Building Garage Location 2463, 1st St. Supt. 
Estimated Actual 
Num- dates dates 
Item 
ber 


Start | Finish | Start | Finish 


Bend and place steel........... 
Mix and place concrete........ 
Remove lors oie Uae tee 


Sash, frames, and trim......... 
Glass and: glazings. .cV ane: 
Roofing and eee REA SE aL 
Plumbing. ere mr ee ey 


Cleaning up av anae oe eee 
Paintings aces © ci ee ee 
Schedule time of completion.... 
Contract time of completion.... 


a a ae ae 
IOoorrwnrnrFPoowonraoamnrwnd 


On a one-course concrete paving job, the time and work 
schedule would include the following items: excavation, rolling . 
subgrade, forming, concreting and finishing, curing, removing 
forms and cleaning up, finishing shoulders, scheduled time for 
completion, contract time for completion. 

On large jobs, delivery schedules are often provided for all of 
the materials used, so that there will be no delays due to lack of 
materials, and, at the same time, there will not be a surplus of 
materials to cover up the work. Labor schedules are sometimes 
made showing the numbers of each of the different classes of 
laborers required on the job for each day. 

Exercises.—State advantages of a time and work schedule for a concrete 
job. 

Prepare a time and work schedule for constructing 1900 lin. ft. of 5-ft. 
concrete sidewalk. All of the walk (slight excavation, forming, and con- 


creting), except curing, must be completed in 5 weeks’ time. State assumed 
dates for schedule time. Excavation work to start on May 1. 


ESTIMATING 175 


JOB 51. PROGRESS REPORTS AND CHARTS 


The superintendent or foreman on a concrete construction job 
should send in to the main office every day a detailed report of 
the progress of the work in his charge. By this method, the 


MATERIALS RECEIVED AND WORK DONE 


ee ee eee COC ALON 
err one SUPERINTENDENT 


MATERIA Se 
GES ey ol Cl eS 
(5 ¢ fo (Sa ae 
Gravel, (cuyds,) 1 ee 
Stone, (pounds) |__| 
Lumber, (Soard ft) 

Nails €Bolts,//os) |__| 


Other Items 


LABORERS] HOURS 
FORMS STEEL 


see EEE 


CLEANED 
STRIP | AND 
REP'D. 


CONCRETE CLEAN 
UP OF 
JOB 


Y 
WW 


° 


Mix | PLACE] FINISH 


S 
Ze 
] 
2 
3 
4 
5 
6 
7 
8 


Gell 
nee 
aa 
ge 
bal 
[ad 
ee 
ie] 
at 


pol 
CEEUBELE 


Ponrmamesemoea = = Sq.ft. See SOIL 
Forms stripped ______—=>=—=———SSs.ft.] Forms cleaned € repd. sq. ft. 
Steel bent fee 105,,| Steelipiaced pee IDS, 
Concrete mixed and placed ____cu.yd.| Concrete surface finished. sq. ft. 
Other work 


Fig. 73.—Superintendents’ daily report form. 


main office is enabled to keep in close touch with the job, and to 
take any needed steps in regard to the supply of materials and 
labor. An examination of the progress reports will show whether 


176 CONCRETE PRACTICE 


the work is progressing at a satisfactory rate in regard to quanti- 
ties and costs. Figure 73 shows a sample form of daily report 
required from the superintendent on a concrete job. This report 
gives a complete summary of materials on hand, received, and 
used, laborers and their work, and the amount of work of different 
kinds performed. 

The daily reports of the superintendent or foreman should be 
checked from time to time by the timekeeper or other official, to 
provide against possible dishonesty and errors. 


PROGRESS CHART FOR CONCRETE WORK 


Estimated| Actual | Percent | 9 = “Concrete ieaease 
Time | Time | of Work Estd.Cost 


olf 
May 29 | 108 2000 | $29000 “fen 


~~ \ ~~ ~~ 


ao 


aS Q 


SSS 

see BS Soe eee eseees 
SKS Reet cee 

~~ oa seanetoneennnseee SPSS 


\ 
recone 


Fic. 74.—Progress chart for concrete work. 


So that the owner, contractor, architect, or engineer may 
clearly and easily visualize the amount of work done, rate of prog- 
ress of the job, and the cost of the work, progress charts are 
prepared and kept up to date. A progress chart is a graphical 
representation of the progress of the work on the job i in question. 
These charts are prepared from the data given in the progress 
reports and must be kept up to date. A progress chart may be 
simple or complicated, and show a few or many details, as the 
case may be. The charts should not be too complicated, or 
contain too much detail, if they are to be read and understood 
by the average person. | 


ESTIMATING Livi 


A simple progress chart for concrete work is shown in Fig. 74. 
The chart includes estimated time, actual time, per cent of work, 
cubic yards of concrete, estimated cost, and actual cost. On this 
one particular job, note that the work lagged for the first 2 weeks 
while the costs were greater than were estimated. During the 
last 2 weeks, the work was speeded up and the job finished on 
time, with an actual cost a little less than that estimated, in 
spite of the fact that the actual concrete required in cubic yards 
exceeded the estimated amount by 5 per cent. 

- Figure 75 shows a time-work schedule for a concrete construc- 
tion job involving excavation, assembling and erecting forms, 


JOB S74... TIME-WORK SCHEDULE 


— JUNE an 


eae 


a 
Excavation ee 
recting Forms 

g ean mel 
Bending and ae) SULLA ies eee UMMLML A: 
Placing Steel 
Mixing and —--] UUtttb ee 
Placi = Concrete -—| | 
= = 

rms 
eo 


pies Wlttte need 7ime "ease eee VLIMTLLLEA a 
inishing ctual Time 
| 


Fig. 75.—Progress chart and time-work schedule. 


bending and placing steel, mixing and placing concrete, form 
removal, and surface finishing. The open (or white lines) show 
the estimated time, and the full black lines show the actual time 
required. This chart could be lengthened and elaborated to 
include as many operations as desired. Another version of this 
chart is to plot the time required with vertical lines, and plot 
the operations horizontally. 

In Fig. 76, the same data were plotted as in Fig. 75, but are 
shown in a different manner. The light lines indicate the 
estimated time, while the actual time is shown by the heavy 
lines. Note that the actual excavation exceeded the estimated 
quantity (due to a bank cave in), while the other actual quanti- 
ties agreed with the estimates. In regard to the time required, 


178 CONCRETE PRACTICE 


the excavation, form removal, and surface finishing each required 
a longer time than was estimated, while the erection of forms and 
steel placing each required less time. 

Another variation of the chart shown in Fig. 76 is to use a light 
black line showing the relation between estimated time and 
quantity of work in percentages, a heavy black line showing 
actual time required, and a heavy red line for costs. If, for any 
operation, the red (cost) line agrees with the heavy black line, 


TIME-WORK SCHEDULE JOB./74... | 


75 


Per Cent 


LEGEND 
Light Lines= Estimated Time 
HeavyLines= Actual Time 


Fig. 76.—Progress chart and time-work schedule. 


the estimated and actual costs agree; if the heavy red line is below 
the heavy black line, the costs are less than were estimated; while, 
if the red line goes above the heavy black line, the costs are more 
than were estimated for the corresponding quantity of work. 
Note that the quantity of work and costs will be expressed in 
the form of a percentage of the estimated total of each. Actual 
quantities and costs may be written on the chart adjacent to 
the corresponding points on the lines, if desired. 


Exercises.—Prepare a progress chart showing the following data in a 
concrete road job: 

Excavation, estimated 12,000 cu. yd., cost $1.25 per cu. yd., start Aug. 1, 
finish Aug. 29. 


ESTIMATING 179 


Forming at sides of road, estimated 11,320 lin. ft., cost 10 cts. per lin. ft., 
start Aug. 3, finish Sept. 38. Steel forms are used and reused throughout 
the job. 

Concrete, estimated 1885 cu. yd., cost $12.85 per cu. yd., start Aug. 4, 
finish Sept. 4. 

Progress Reports—totals are given. 

Excavation, start Aug.1; Aug. 8, 2750 cu. yd., cost $3680; Aug. 15, 5450 
cu. yd., cost $7025; Aug. 22, 8725 cu. yd., cost $11,100; Aug. 29, 11,200 cu. 


* yd., cost $13,900; Sept. 1, finish, 12,320 cu. yd. cost $15,200. 


Forming at sides, start Aug. 4; Aug. 8, 1420 ft. cost $151; Aug. 15, 3230 ft., 
cost $347; Aug. 22, 6170 ft., cost $628; Aug. 29, 9250 ft., cost $930; Sept. 3 
finish, 11,320 ft., cost $1116. 

Concreting, start Aug. 5; Aug. 8, 228 cu. yd., cost $8030; Aug. 15, 531 
cu. yd., cost $6950; Aug. 22, 1020 cu. yd., cost $13,420; Aug. 29, 1530 cu. yd., 
cost. $19,600; Sept. 4, finish, 1891 cu. yd., cost $24,150. 


SECTION V 


LABORATORY METHODS 


WORK IN THE LABORATORY 


Purpose of Laboratory Work.—The purpose of this labora- 
tory work is to give the student a general idea of the physical 
properties of cements, aggregates, mortars, and concretes, and 
the various ways of testing them. The student is not expected 
to become an expert tester upon the completion of the course, 
but he will be expected to know how the different tests should 
be made. Considerable experience is necessary before anyone 
can become an expert in the testing of cements and concretes, 
and in the correct interpretation of the results. It is only by 
close observations of the rules and specifications that even this 
may be accomplished. 

Apparatus.—Each student will be held responsible for all 
apparatus assigned to him. In general, all apparatus needed 
during the laboratory period should be secured from the instruc- 
tor at the beginning of the period. All tools, apparatus, tables, 
etc., should be cleaned immediately after using, and all of the 
waste material should be deposited in the waste boxes provided 
for that purpose. Waste material should not be thrown on the 
floor. Neatness and cleanliness are important elements in all 
laboratory work. 

Making Specimens.—The methods of mixing and molding 
given in the standard methods and specifications will be followed 
in all tests as far as practicable. At the beginning of the 
first laboratory class, the instructor should illustrate the methods 
of preparing briquette molds and the mixing and molding of 
briquettes. 

Curing Specimens.—All cement, mortar, and concrete speci- 
mens will be removed from the molds, marked, and stored accord- 
ing to the requirements of the standard specifications. 

180 


LABORATORY METHODS 181 


Marking Specimens.—Each specimen, at the time it is made, 
or when it is removed from the molds, should be marked, so that 
it can be identified as to owner, composition, and test. Bri- 
quettes should always be marked on the ends. When in doubt, 
consult the instructor in regard to the proper way of marking 
the specimens. 

Testing.—A student must not use any machine until its prin- 
ciples of operation have been explained to him by the instructor. 
A good rule for the student is: Do not use any testing machine 
_ unless the instructor is present and has given permission. In 
testing, follow the instructions given in the job sheets and in 
the standard methods and specifications. Good results can be 
secured only when the rules governing the operation of the 
testing machine are strictly followed. 

Notebook.—Each student should keep a notebook for use 
in the laboratory. In this notebook, the student should record 
the date of making, composition, and marks of the specimens, 
the dates on which the specimens are to be tested, the data 
obtained during the tests, and all other observations and data 
that may be of usein writing reports or in making future 
experiments. 

Efficiency.—In the laboratory students should: (1) try to do ’ 
good work, and (2) try to do the work in as short a time as prac- 
ticable. That is, students should try to become both good 
workers and fast workers. ‘The instructor may, at various times, 
instruct students in their work so that their efficiency will be 
improved. 

LABORATORY REPORTS 


Laboratory Reports.—The laboratory reports required may 
be written either in a laboratory report book or on loose sheets of 
typewriter-size paper, and the sheets comprising each report 
fastened together with clips. If report books are used, the paper 
in them should preferably be cross-section paper, of about 5 
divisions per inch. If loose sheets are used, it is advisable to fasten 
the sheets inside manila folders. The front cover page of this 
folder should have on it the title of the test, the student’s name, 

the date that the report is due, and any other information 
- required by the instructor. All reports should be neatly written 
in ink or typed. 


182 CONCRETE PRACTICE 


Outline.—The standard outline for a laboratory report is as 
follows: 


1. Title 6. Computations 

2. Object 7. Curves 

3. Apparatus (and sketches) 8. Conclusions 

4. Method 9. Answers to questions 
5. Data 


Title-—The title should indicate the subject of the experiment 
or test. In general, the heading given the experiment on the job 
sheet will be sufficient. 

Object.—This is a brief, concise statement of the purpose of the 
experiment. . 

Apparatus.—Under this heading include a list of apparatus 
used and, when required, a neat sketch of some piece of the 
apparatus. Any. special apparatus used should be briefly 
described. 

Method.—Describe briefly how the test was made. If the 
method is a standard one that has been described in the text, a 
reference to the text (giving the page number) will be sufficient. 

Data.—The data should be tabulated in a neat systematic form. 
All data should be carefully checked before handing in the 
report. ; 

Computations —Sample computations should be included in 
the report, to show how the main results were obtained from the 
data. The formulas used and the numerical substitutions in 
them should always be given in full. 

Results of computations should be accurate to 1 per cent. The 
properties of the specimens tested will rarely be the same as 
the average properties given in the texts. Results differing 
greatly from the average values frequently indicate errors in 
computations. 

Curves.—Curves should be drawn on cross-section paper of the 
same size as the report paper, and having 5, 10, or 20 divisions 
perlinealinch. ‘The points determining the curve should be shown 
in small circles (small triangles, squares, etc., may be used, if there 
be more than one curve). The curve should be carefully drawn 
with either a straight or a curved ruler. Medium and fine lines 
are better than heavy ones. When there are only a few points, 


LABORATORY METHODS 183 


straight lines should be drawn connecting these points; but when 
there are many points, a smooth curve should be drawn. The 
scales of the coordinates should be plainly marked. The curve 
sheet should show the title of the experiment and the main 
results. 

Conclusions.—The conclusions should contain a summary of 
the main results and important facts obtained from the test. 

Questions.—All questions asked should be answered in full. 


JOB 52. INSPECTION AND SAMPLING OF PORTLAND CEMENT 


Object.—To inspect and sample a shipment of portland cement. 

Significance—The securing of a representative sample of 
cement is essential, if the test results are to indicate correctly the 
properties of the cement. 

References.—Appendix 1. 

Inspection.—Observe if the shipment is stored in such a manner 
that it can be easily inspected and identified, and also observe if 
the building is weather-tight, and the cement protected from 
dampness. 

The cement may be in bulk, barrels, or bags. If in barrels 
or bags, note if the brand of the cement and the name of the 
manufacturer are plainly marked thereon. , 

~Check the weights of several bags (or barrels), and note if the 
weight requirements of the specifications are met. 

Observe if the cement contains lumps, and if the lumps are 
hard or soft. Soft lumps are comparatively harmless. 

Sampling.—Secure a sample as directed in Secs. 16 to 19, 
inclusive, of Appendix 1. If the cement is sacked, a sample may 
be obtained by inserting a piece of split tubing through a flap in 
the bottom of a sack. Metal cans with tight covers or heavy 
paper sacks are suitable containers for cement samples. The 
container should be marked so that the sample can be correctly 
identified. 

Report.—Prepare a brief report. This report should include 
the name of the brand and the manufacturer of the cement, size 
of shipment (approximate or actual number of bags or barrels), 
the place of storage, the name of the inspector, the date of the 
inspection, the results of the inspection as to proper storage, 
lumps, weights of barrels or bags, etc., whether the sample was an 


184 CONCRETE PRACTICE 


individual or composite one, size or weight of the sample, the 
marking on the container of the sample, and any other informa- 
tion that the inspector deems essential. 


JOB 58. NORMAL CONSISTENCY OF PORTLAND CEMENT 


Object—To determine the percentage of water required to 
make a cement paste of normal consistency. 

Significance.—The correct percentages of water must be used 
when mixing the neat cement pastes and the cement mortars, or 
the test results will not be reliable. 

References—Appendix 1. 

Materials —Portland cement. Note the brand. 

Apparatus.—Scales, trowel, graduated cylinder for measuring 
water, watch, Vicat apparatus, etc. 

Vicat Method.—¥Follow method given in Sec. 39 of Appendix 1. 
Use about 23 per cent of water for the first trial paste. Record 
penetration of rod. If this paste is not of normal consistency, 
make other trial pastes with varying percentages of water until 
the normal consistency is obtained. 

Ball Method. (Old U.S. Government Method).—After mixing 
a trial paste by the previously described method, quickly form 
a 2-in. ball of the neat cement paste. Drop the ball, from a 
height of 2 ft., upon the table top. The cement paste is of nor- 
mal consistency when the ball does not crack and does not flatten 
more than one-half of its original diameter. Make trial pastes 
with varying percentages of water until the normal consistency 
is obtained. 

Notr.—When a trial paste of normal sonst has been 
obtained, this paste may also be used for determining the time of 
set and for making the pats for the soundness test. 

Report.—Prepare a tabulation showing the percentages of 
water used, and the corresponding penetrations of the Vicat rod 
or the corresponding flattenings of the diameter (expressed 
approximately in tenths of the original diameter) in the ball test. 
Note the mixtures which cracked when they were dropped 1 in the 
ball test. 

Questions.—If both methods were used, which method gave the 
best results? Why? 


LABORATORY METHODS 185 


How will the amount of water in the trial paste affect the 
strength and setting time of the cement? | 

Why do different cements require different percentages of 
water to give normal consistency? 

The quantity of cement to be mixed at one time should not be 
less than 5000 g. or more than 1000 g. Why? 


JOB 54. TIME OF SETTING FOR PORTLAND CEMENT 


Object—To determine the time required for initial and final’ 
set of a sample of portland cement. 

Significance.—The object of this job is to determine the time 
which elapses from the moment water is added until the paste 
ceases to be plastic (called the initial set), and also the time which 
elapses before the paste acquires a certain degree of hardness 
(called the final set or hard set). The former is the more impor- 
tant, since, with the commencement of setting, the process of 
crystallization begins. As a disturbance of this process may 
cause a loss of strength, it is desirable to complete the operation 
of mixing, molding, or incorporating the mortar or concrete into 
the work before the initial set occurs. 

References.—Appendix 1, and See. I. 

Materials —Portland cement. Note the brand. 

Apparatus.—Vicat apparatus or Gillmore needles and other 
apparatus, as in the preceding job. 

Method.—Follow the directions given in Sec. 45 to 49 inclusive 
of Appendix 1. Either the Vicat apparatus or the Gillmore 
needles may be used for determining the time of set. Be sure 
to note the time when the water was first added to the cement. 

Report.—Note the time required for the initial and final sets 
of this sample of portland cement. 

Questions.—Did this sample of portland cement pass the 
specifications for the time of setting for portland cement? 

Which method of test (Vicat or Gillmore) do you prefer? 
Why? 

What is the effect on construction work of using a quick-setting 
cement? Of using a slow-setting cement? 

If a cement having a flash set is used in concrete, how should 
this concrete be mixed to overcome the effect of the flash set? 


186 CONCRETE PRACTICE 


JOB 55. SOUNDNESS TEST OF PORTLAND CEMENT 


Object.—To determine the soundness of a sample of portland’ 
cement. 

Significance.—Portland cement must be sound (that is, must 
not swell, disintegrate, or crumble) if it is to be used on construc- 
tion work. The steam test quickly brings out those qualities 
which tend to destroy the strength and durability of the cement. 

References—Appendix 1 and Sec. I. 

Materials —Portland cement. Note the brand. 

Apparatus.—Scales, graduated glass cylinder for measuring 
water, trowel, watch, glass plates about 4 in. square, and the 
special apparatus for the steam test,etc. See Fig. 3 of Appendix 1 
for an illustration of this special steam test apparatus. 

Method.—Follow the method given in Secs. 42, 48, and 44 of 
Appendix 1. Note that it takes some practice and skill to make 
a good, smooth, neat cement pat of the correct size and shape. 

Testing.—After the water is boiling in the steam test apparatus, 
place the day-old pat in the apparatus, as directed in Sec. 43 
of Appendix 1, and keep the pat there for 5 hrs. 

Report.—State the results obtained from the test. 

Questions.—Did this sample of portland cement pass the sound- 
ness test specifications? 

Why should the pat have thin edges? 

Is the cement sound if the bottom surface of the pat is found 
to be curved or warped after the conclusion of the steam test? 

Does the passing of the soundness test always indicate a sound 
cement? 


JOB 56. STANDARD TENSION TEST 


Object—To determine the tensile strength of the standard 
portland cement mortar. | 

Significance—Tensile tests on the standard mortar give a 
fairly good indication of the strength qualities of a portland 
cement. 

References.—Appendix 1 and Sec. I. 

Materials—Portland cement and standard Ottawa sand. 
Note the brand of the cement. 

Apparatus.—Two 3-gang briquette molds, scales, graduated 
glass cylinder, trowel, watch, etc. 


LABORATORY METHODS 187 


Method.—Follow the method given in Secs. 36, 37, and 50 to 61, 
inclusive, of Appendix 1. Make six briquettes of 1:3 mortar 
(1 part of cement to 3 parts of sand by weight). About 250 g. 
of cement and 750 g. of sand are required for six briquettes. 
Obtain the percentage of water from Table 1 of Appendix 1. 
The amount of water needed is found by multiplying the total 
weight of the cement and sand by the percentage given in the 
table. 
Storage.—One day in moist air and then in water as directed 
in Appendix 1. 

Testing.—Break three briquettes at an age of 7 days, and the 
remaining three at an age of 28 days. Record results. 

Reports.—Tabulate the individual and average results at each 
age, together with the brand of cement, percentage of water, etc. 

Questions —Did this sample of portland cement pass the 
standard specifications for strength tests? 

Does the amount of water used in making standard mortar 
briquettes affect their strength? 

Why should the mortar be thoroughly mixed? 

What is the area of the smallest cross-section of a briquette? 

How would storage in air affect the strength of the briquettes? 


- 


JOB 57. FINENESS OF PORTLAND CEMENT 


Object—To determine the fineness of a sample of portland 
cement. 

Significance.—The extremely fine powder or flour in portland 
cement is the important cementing element. As there are no 
sieves fine enough to determine satisfactorily the percentage of 
this flour, the fineness test only tends to indicate the soundness 
and strength of the cement. Usually a coarse cement will 
show a low mortar strength, and will often fail to pass the 
soundness test. 

References—Appendix 1 and Sec. I. 

Materials.—Portland cement. Note the brand. 

Apparatus.—Standard 200-mesh fineness sieve with cover 
and bottom, and scales sensitive to about 0.01 g. 

Method.—Follow the method given in Appendix 1. The scales 
should be leveled in a place where they will not be affected by 


188 CONCRETE PRACTICE 


air currents. Results should be noted to the nearest tenth of 
1 per cent (nearest 0.05 g.). 

Report.—State the results obtained. 

Question.—Did this sample of portland cement pass the stand- 
ard specifications for fineness of cement? 

If the same sample of portland cement was used in Jobs 52 
to 57, inclusive, and if the soundness, set, tensile strength, 
and fineness tests only were required, would this portland cement 
be considered as satisfactory for use'in concrete for construction 
purposes ? 

Norr.—Jobs 52 to 57, inclusive, include all of the tests that are 
usually asked for when testing a sample of portland cement. 
In some instances, the fineness test is omitted. 


JOB 58. INSPECTION AND SAMPLING OF AGGREGATES 


Object.—To inspect a source of supply for concrete aggregates, 
and to secure samples. 

Significance—Before beginning any large concrete job it is 
important that the engineer should know about the aggregates 
to be used, especially in regard to quantity, uniformity of supply, 
grading, and other qualities. 

References.—Sec. I. 

Method.—The following information should be obtained in 
regard to all stone quarries or gravel pits inspected: name of 
owner, locality, approximate quantity available, character of 
overburden or stripping, length and character of haul to the job, 
or to the shipping point. 

Crushed Stone from Commercial Quarries.—In addition to the 
above information, data should be recorded concerning the 
crushing and screening plant, such as number and size of crushers, 
size and shape of screen openings, daily capacity of plant, number 
and size of storage bins, and sizes of crushed stone sold. When 
practical, samples of fresh, unweathered rock may be taken from 
the quarry face. Samples of crushed rock may be taken from the 
stock piles, bins, loading chutes, cars, or boats. It is advisable 
to take the samples from the cars or boats while they are being 
loaded—the samples being taken at different times and then well 
mixed to make a composite sample. If samples are taken while 
the cars or boats are being unloaded, samples should be obtained 


LABORATORY METHODS 189 


from the top, middle, and bottom of each car or boat. The 
weight of the sample of crushed rock should be from 50 to 100 lb. 

Sand and Gravel.—Very few sand and gravel deposits are uni- 
form throughout, hence it is often necessary to take separate 
samples from several parts of the pit, if correct information in 
regard to the bank run is to be obtained. Note if any of the top 
soil has fallen into the pit, if there is any clay in the pit, and if 
there are pockets of fine or coarse material. In pits where there 
are screening and washing plants, the samples should be secured 
from the tops and the loading chutes of the bins, care being taken 
to obtain representative samples. If it is not practical to visit 
the pit or plant, samples may be taken from the top, middle, and 
bottom of the car or boat when unloading. Samples of bank-run 
gravel should be 100 lb. or more (the sample should provide at 
least 50 lb. of gravel after screening). Samples of gravel should 
contain at least 50 lb., and samples of sand at least 20 Ib. A 
sample should be placed in a tight box or bag; and should be 
carefully tagged, so that it can be identified. It is a good plan to 
place an extra marked tag inside of the container. 

Quartering Method.—All samples should be brought to the 
laboratory for observation and testing. If any sample is too 
large, it may be reduced in size by the quartering method. The- 
sample should be first thoroughly mixed on a tight platform or 
floor, and then spread into a circular pile and divided into four 
parts or quarters. Two of the opposite quarters are shoveled 
away, and the process of mixing and quartering repeated until the 
sample is reduced to the desired size. 

Report.—Write a brief report describing the crushed stone or 
gravel plant visited. A complete investigation would also 
include reports of the tests made on the samples such as sieve 
analyses, silt test, colorimetric test, and, when time permits, 
strength tests of concrete made from the aggregates. 


JOB 59. UNIT WEIGHT OF CONCRETE AGGREGATES 


Object—To determine the weight per cubic foot of fine and 
coarse concrete aggregates. 

Significance—When designing concrete mixes by Beetle 
methods, it is necessary to know the unit weights of the aggre- 


190 CONCRETE PRACTICE 


gates, so that the proportions of the concrete mixes may be 
correctly computed. 

References —Appendix 2 and See. I. 

Materials—Room-dry samples of both fine and coarse aggre- 
gates. 

Apparatus.—Tamping rods and metal measures described in 
Appendix 2. If these measures are not available, strong and 
tight wooden boxes of 14 cu. ft. and 1 cu. ft. capacity will usually 
prove to be satisfactory. 

Method.—Follow the method given in Appendix 2. After the 
unit weight has been found for a room-dry sand, thoroughly 
dampen this sand by adding 5 per cent of water by weight, and 
then mix the sand and water. Then determine the unit weight 
of the dampened sand. 

Report—Make a tabulation showing the various materials 
tested, and the resulting weights per cubic foot. 

Questions.—Does the dampened sand weigh more or less than 
the dry sand? Why? 

If the proportions for a concrete mix were based on dry sand, 
what would be the effect on these proportions of using damp 
sand? 


JOB 60. SIEVE ANALYSIS OF AGGREGATES 


Object—To make sieve analyses of various fine and coarse 
aggregates. 

Significance.—As several of the methods of proportioning 
concrete mixes depend upon the grading of the aggregates, it is 
necessary first to make sieve analyses of the aggregates. 

References.—Appendix 8 and Sec. I. 

Materials—Samples of different fine and coarse aggregates 
which are room dry. 

Apparatus.—Scales which are sensitive to about 14 g., and a 
set of standard sieves as described in Appendix 3. These sieves 
are practically the same as the Tyler series of sieves, in which 
the opening of any sieve is double that of the next lower sieve. 

Method.—Follow the method outlined in Appendix 3. If 
there is any doubt about a sieve not being standard, that sieve 
may be checked by counting the number of openings per linear 


LABORATORY METHODS 191 


inch in both directions, and by measuring the diameter of the 
wire. 

Computations—For each aggregate tested, compute the 
percentage passing each sieve, and also compute the percentage 
retained on each sieve. Compute the fineness modulus of each 
of the aggregates. | 

Report—Make a tabulation showing the sieve number or 
Size, size of sieve opening, and, for each aggregate tested, the 
percentage passing each sieve, the percentage retained on each 
sieve, and the fineness modulus. 

Questions.— Which of the fine aggregates passed the specifica- 
tions for fine aggregates as given in the text? (See Sec. I, page 
11.) Which of the coarse aggregates passed the specifications 
for coarse aggregates as given in the text? (See Sec. I, page 
15.) Why should the materials be dry when sieved? 


JOB 61. SIEVE ANALYSIS CURVES 


Object—To plot curves showing the sieve analyses of various 
fine and coarse aggregates. 

Significance.—A sieve analysis curve for an aggregate enables 
an engineer to tell easily if that aggregate is well graded or not. 

References.—Sec. I and Job 60. 

Method.—On cross-section paper having, preferably, 10 divi- 
sions per lin. in., plot a sieve analysis curve for each of the aggre- 
gates tested in Job 60. Use one sheet of cross-section paper for 
the fine aggregates, and another sheet for the coarse aggregates. 
Plot percentages passing sieves to a vertical scale (ordinates), 
and size of sieve openings to a horizontal scale (abscissae). 
Consult the instructor in regard to the proper scales to use. See 
Appendix 3 for the sieve openings of the various sieves. 

Report.—With the curve sheets, include a brief description of 
the aggregates tested. 

Questions.—Judging by the curves, which aggregates appear to 
be well graded? 

Which aggregates seem to be suitable for use in concrete mixes? 


JOB 62. VOIDS IN FINE AND COARSE AGGREGATES 


Object—To determine the voids in samples of various fine and 
coarse aggregates. 


192 CONCRETE PRACTICE 


Significance—Other things being equal, a denser aggregate 
will make a denser and better concrete. 

References.—Sec. I. 

Materials —Room-dry samples of various fine and coarse 
aggregates. 

Apparatus.—Scales capable of weighing to 200 lb. and sensitive 
to !4 lb., a water-tight metal measuring box or strong pail having 
a capacity of from 14 to 1 cu. ft., and an iron tamping rod like 
that described in Appendix 2. __ 

Method.—Weight the empty measure or pail. Fill it level 
full of water, and weigh it again. The weight of the water 
divided by 62.355 (the weight of 1 cu. ft. of water in Ibs.) will give 
the volume of thé measure in cubic feet. Be sure that the top 
of the measure is level when it is filled with water. 

Fill the measure with an aggregate, and tamp according to 
the method described in Appendix 2. Weigh the measure and 
aggregate. Pour water slowly in the aggregate until the measure 
is level full. Then weigh measure, aggregate, and water. Empty 
and clean the measure. 

Repeat the process with each of the other aggregates. 

Computations.—Percentage of Voids.—The total weight of 
the measure, aggregate, and water, minus the weight of the 
measure and aggregate, gives the weight of the water in the voids. 
The volume of the voids in the aggregate is equal to the weight 
of the water in the voids divided by 62.355. The ratio of the 
volume of the voids to the volume of the aggregate (same as 
the volume of the measure) multiplied by 100 gives the percent- 
age of voids in this aggregate. 

Weight per Cubic Foot.—The weight of the dry aggregate 
in the measure in pounds, divided by the volume of the measure 
in cubic feet, gives the weight per cubic foot of the aggregate. 

Approximate Specific Gravity——The approximate specific 
gravity is equal to the weight of the dry aggregate in the measure 
divided by the difference between the volume of the aggregate 
(same as the volume of the measure) and the volume of the 
voids. 

Report.—Prepare a tabulation showing all of the data taken 
and the results obtained. Include in the report the computation 
for the volume of the measure. , 


LABORATORY METHODS 193 
The following is a sample tabulation: 


Material | Crushed | Gravel 


Sand | Ete. 


Weight of measure and aggregate in 


Weight of measure, aggregate, and 

Webel DOUNIS. cress... see ees 
Weight of water in pounds......... 
Volume of voids in cubic feet....... 
Weight of aggregate per cubic feet. .. 
Approximate specific gravity....... 


Questions.—Compare the weights per cubic foot found in this 
job with the weights per cubic foot found in Job 59. | 
Why does an aggregate composed of particles of a uniform size 
have a larger percentage of voids than an aggregate composed of 
particles of several sizes? 
. Why should the top of the measure or pail be level when it is 
filled with water? 


JOB 63. SILT IN FINE AGGREGATE 


- Object.—To determine the amount of silt in a sample of fine 
aggregate. 

Significance.—lIt is advisable to know the proportion of silt in 
a fine aggregate, because a comparatively large amount of silt 
often indicates the presence of organic impurities. A small 
amount of silt may ball up in a mortar, and tend to keep the 
cement from hardening. In some instances, however, a small 
amount of silt well distributed throughout a concrete mix tends 
to make a lean concrete more dense and waterproof. 

References.—Appendix 4 and Sec. I. 

Materials —One or more samples of fine aggregate. 

Apparatus.—A pan or vessel, such as is described in Appendix 
4, scales, and a 500-c.c. glass graduate. 

Method.—Follow the method given in Appendix 4. 

An approximate method is to fill the 500-c.c. graduate up to 
the 200-c.c. mark with fine aggregate. Then water should be 
added until the 400-c.c. mark is reached. The aggregate and 
water should be agitated vigorously with a stiff wire or glass rod 


194 CONCRETE PRACTICE 


for a time of 1 min. The graduate should then be allowed to 
stand until the settlement is complete. Measure the relative 
height of the fine aggregate and silt. Compute the percentage 
of silt by volume. Note that the silt does not weigh as much as 
the fine aggregate, hence the percentage of silt by volume is 
greater than the percentage of silt by weight. 

A rough field method is to rub a small amount of the fine 
ageregate in the palm of the hand, and note if it causes a dark 
spot or stain on the hand. Such a stain indicates silt. 

The presence of a comparatively small amount of silt may 
be determined by the eye, by observing if the sample of fine 
aggregate appears to be dirty, and if the grains seem to be coated. 

Report—Make a tabulation showing the different samples 
tested and the percentages of silt found. 


JOB 64. COLORIMETRIC TEST OF A FINE AGGREGATE 


Object—To determine the presence of injurious organic com- 
pounds in a sample of fine aggregate. 

Significance.—As a very small amount of organic matter in the 
fine aggregate may greatly reduce the strength and soundness of 
the concrete, it is important to detect the presence of organic 
matter in the aggregate. Silt is apt to contain organic matter, 
consequently it is not advisable to use a fine aggregate contain- 
ing more than 3 per cent of silt as a concrete aggregate, without 
first testing this aggregate for the presence of injurious organic 
compounds, or making strength tests on a mortar made from this © 
fine aggregate. 

References.—Appendix 5 and See. I. 

Materials—Samples of fine aggregates. 

A pparatus.—Bottles and solutions as described in Appendix 5. 

Method.—Follow the method described in Appendix 5. 

A very dark orange color or a dark brown color indicates that 
the fine aggregate has an appreciable amount of injurious organic 
matter. A light yellow or white color indicates that there is very 
little injurious organic matter present. In general, solutions 
darker than the standard solution indicate the presence of 
injurious organic matter. In doubtful cases strength tests of a 
mortar or concrete (made with the aggregate in question) should 
be made before arriving at a final decision. 


LABORATORY METHODS 195 


heport.—Report on all fine aggregates tested giving the color of 
the liquid in the bottle in each case. State which aggregates are 
acceptable for use in concrete mixes. 


JOB 65. BULKING EFFECT OF WATER IN SAND 


Object.—To observe the bulking effect of water in sand. 

Significance—Comparatively small percentages of water (from 
4 to 8 per cent) added to a dry sand will cause the sand to increase 
in volume. A knowledge of this bulking effect is essential when 
designing concrete mixes in which wet sand is used. 

References.—Sec. I. 

Materials—A sample of room-dry sand, or, preferably, a 
sample of sand dried to a constant weight. 

Apparatus.—Scales, 500-c.c. glass graduate, glass or metal rod 
for tamping. 

Method.—1. Weigh out sufficient drys and to fill the 500-c.c. 
graduate about half full. Place the sand in the graduate in about 
three equal layers, tamping each layer as described in Appendix 2. 
Record the volume of the sand in the graduate. 

2. Weigh out an equal amount of dry sand as before, add 2 
per cent of water by weight, mix sand and water thoroughly, tamp 
in graduate as before, and record the volume. 

3. Repeat the process using 4, 6; 8, and 10 per cent of water. 
Record the results. 

4. Make one trial with enough water just to flood or inundate 
the sand. Record percentage of water used, and the resultant 
volume. 

If sufficient graduates are available, each mixture of sand and 
water can be left in its respective graduate. Placing these gradu- 
ates in order in a row will illustrate the bulking effect of water 
very nicely. 

Report.—Make.a tabulation showing the percentages of water 
added and the percentages of increase in volume (bulking) of the 
sand. 

Questions—What percentage of water appeared to give the 
maximum bulking effect for this particular sand? 

How did the volume of the inundated sand compare with the 
volume of the dry sand? 


196 CONCRETE PRACTICE 


JOB 66. TENSILE STRENGTH OF CEMENT MORTARS MADE WITH 
DIFFERENT SANDS 

Object—To compare the tensile strength of mortars made with 
different sands. 

Significance.—It is often advisable to make strength tests on 
mortars made from sands to determine if the sands are suitable 
for mortars and concretes. 

References.—Sec. I. 

Materials —Portland cement and samples of fine, coarse, and 
well-graded sands. Note brand of cement. 

Apparatus.—Scales, three 3-gang briquette molds, glass 
graduate, watch, trowel, etc. 

Method.—Make. three briquettes using each kind of sand. 
Follow method given in Appendix 1 for mixing and molding 
briquettes. All mixes are 1:3 by weight. About 125 g. of 
cement and 375 g. of sand are required for three briquettes. 
Knowing the percentage of water required for normal consistency 
of the cement, obtain the percentage of water for the 1:3 mortar 
from Table 1 of Appendix 1. It may be necessary slightly to 
vary the values given in the table for the different sands in order 
to get a workable mix. 

Storage.—One day in moist air and then in water. 

Testing.—Break all briquettes at an age of 28 days. If time 
does not permit, the briquettes may be broken at 7 or 14 days. 
Weigh each set of briquettes before testing. 3 

Report.—Tabulate the individual and average results for each 
sand together with the brand of cement, kind of sand, percentage 
of water, weights of briquettes, ete. Include in this tabulation 
the results of the 28-day tensile test made on the 1:3 mortar of 
standard Ottawa sand. If available, include the weights per 
cubic foot of the sands. 

Questions — Which sand made the strongest mortar? Why? 

Which sand made the heaviest (or densest) briquettes? 

Were the heaviest briquettes the strongest? 


JOB 67. TENSILE STRENGTH OF CEMENT MORTARS OF DIFFER- 
ENT PROPORTIONS 


Object.—To determine the effect of varying the amount of the 
cement on the tensile strength of the mortar. 


LABORATORY METHODS 197 


Szignificance—Other things being equal, the greater the pro- 
portion of cement, the greater the strength of the mortar. 

References.—Sec. I. 

Matervals—Portland cement and a fairly well-graded sand. 
Note the brand of cement. 

Apparatus.—Scales, three 3-gang briquette molds, glass 
graduate, watch, trowel, etc. 

Method.—¥ollow the method of mixing and molding given in 
Appendix 1, and make nine briquettes as follows: 

Three briquettes, 1:1 mix, using 250 g. of cement and 250 g. 
of sand. 

Three briquettes, 1:3 mix, using 125 g. of cement and 375 g. 
of sand. 

Three briquettes, 1:5 mix, using 80 g. of cement and 400 g. 
of sand. 

Compute the percentage of water required for each mix by the 
formula: 


Percentage of water = 


By eg t 65 


Where P = percentage of water for normal consistency of 
cement, and 
nm = number of parts of sand to one of cement. 

The percentage of water is based on the combined weight of 
the cement and the sand. For example, if the cement requires 
24 per cent of water for normal consistency, the percentage of 
water for a 1:3 mortar is found by substituting in the formula as 
follows: 

Percentage of water for a 1:3 mortar = 


eet se = + 6.5 = 10.5 per cent. 


If there were 500 g. of cement and sand, the amount of water 
needed would be 500 X 10.5 per cent or 52.5 c.c. (or grams). 
Storage.—One day in moist air and then in water. 
Testing.—Break all briquettes at an age of 28 days. 
Report.—Tabulate the individual and average results for each 
mix, together with the brand of cement, kind of sand; proportion 
of mix, percentage of water, etc. , 
Question.—What conclusions may be drawn from the results 
of this test? 


198 CONCRETE PRACTICE 


JOB 68. CONSISTENCY OF PORTLAND CEMENT CONCRETE 


Object—To determine the consistency of a mix of portland 
cement concrete by means of the ‘‘slump”’ test. 

Significance.—The best results are obtained in concrete work 
when the least amount of mixing water is used that will give a 
concrete of just workable consistency for the job in question. 
Concrete that is to be used in floors and thin walls requires a 
little more mixing water than if it were to be used in heavy foun- 
dations or massive concrete work. 

References —Appendices 7 and 8 and Jobs 9 to 13 inclusive. 

Materials—Portland cement and room-dry fine and coarse 
aggregates. The maximum size of the coarse aggregate should 
not be more than 1/4 in. Note the brand of the cement and the 
kinds of the aggregates. 

Apparatus.—Measuring boxes, scales, water-tight mixing plat- 
form, shovels, trowels, pail, watch, and slump test apparatus 
as described in Appendix 7. If a concrete mixer is used, the 
mixing platform is not needed. 

Method.—Follow methods given in Appendix 7 for the slump 
test, and in Appendix 8 for mixing a batch of concrete by hand. 
In laboratory work, the amount of water is frequently given as 
a percentage of the weight of the cement or of the total weight of 
the dry materials. On the job, the amount of mixing water 
is usually given as the number of gallons of water per sack of 
cement. Thus the water may be either weighed or measured. 
Either way is satisfactory, provided the scales and measures 
are accurate. 

If either, or both, of the aggregates are wet, the amount of 
water present in the aggregates must be determined and allow- 
ance made. The amount of water in any aggregate may be 
found by weighing a sample of the aggregate, drying this sample 
to constant weight, and weighing again. The difference between 
the two weights gives the amount of water that was present. 
If the aggregates are thoroughly room dry, the amount of water 
in the aggregate is probably quite small and may be neglected. 

Make a batch of 1:2:4 concrete by volume, using just enough 
water to give a mix of workable consistency. Perform the slump 
test. Record the proportions of the mix, amount of water used, 
and observed slump in inches. 


LABORATORY METHODS 199 


Report.—Include in the report the brand of cement, kinds of 
aggregates, proportions of mix, amount of water used, slump, 
and any other data of importance. 

Questions—How many gallons of water per sack of cement 
were required? 

What is the water cement ratio (ratio of volume of water in 
cubic feet to volume of cement in cubic feet in this mix)? 

If the weights per cubic foot of the aggregates are available, 
what would be the proportions of the mix by weight? Assume 
that 1 cu. ft. of cement weighs 94 Ib. 

What should be the maximum slump permitted for: 

1. Mass concrete? 

2. Reinforced concrete of 

a. thin, vertical sections and columns? 
b. heavy sections? 
c. thin, confined horizontal sections? 

3. Mortars for floor finish? 


JOB 69. PROPORTIONING CONCRETE BY ARBITRARY 
PROPORTIONS 


_ Object—To proportion concrete mixes. by arbitrary 
proportions. 

Stgnificance.-—Proportioning concrete mixes by volume by 
arbitrary proportions was (and still is in many localities) the 
generally accepted method of proportioning. At the present 
time this method is used for most small jobs, but is being super- 
ceded by more scientific methods for the large jobs. 

References——Appendices 7 and 8; Sec. I; Jobs 1, 2, and 10 
to 13, inclusive. 

Materials —Portland cement and room-dry fine and coarse 
ageregates. The maximum size of the coarse aggregate should 
not exceed 144 in. Note the brand of the cement and the kinds 
of aggregates. | 

A pparatus.—Measuring boxes, scales, mixing platform, shovels, 
trowels, and six (or nine) cylinder molds 6 in. in diameter and 
12 in. high, with machined metal base plates and capping plates. 
A hydraulic compression testing machine (or a universal test- 
ing machine), scales, calipers, and ruler. 


200 CONCRETE PRACTICE 


-Method.—Quantities.—Using Fuller’s rule (Job 12) compute 
quantities of cement, fine and coarse aggregates to make two 
(or three) cylinders of concrete for each of the following mixes 
by volume: 1:2:4, 1:3:6, and 1:4:8. 

Consistency.—Use enough water in each mix to give a consist- 
ency having a slump of 6 in. Note amount of water required 
in each case. | 

Norsr.—If a compression testing machine and cylinder molds 
are not available, this job may be discontinued at this point. 

Mixing and Molding.—Mix and mold each set of cylinders 
according to the method given in Appendix 8. The cylinder 
molds and base plates should be thoroughly oiled with a heavy 
oil before the concrete is placed in them. The capping must 
be carefully done if consistent results are to be obtained. 

Storage.—Store cylinders as directed in Appendix 8. 

Testing.—When the cylinders are 28 days old, weigh them, 
measure their diameter and height, and test them as directed 
in Appendix 8. Note the maximum (ultimate) load applied 
to each cylinder, and the manner of failure. For each cylinder, 
compute the weight per cubic foot, cross-sectional area, in square 
inches, and the unit ultimate compressive strength. 

Report.—Tabulate all data and results including the propor- 
tions of each mix, water-cement ratios, unit weights of materials 
(if available), weights and dimensions of the cylinders, maximum 
loads applied, unit strengths, ete. 

Questions.—If the unit weights of the aggregates are available, 
what are the proportions of the different mixes by weight? 

How many gallons of water per sack of cement were used in 
each mix? 

Did there appear to be any relation between the unit ultimate 
compressive strength, and the weight per cubic foot of cylinders 
of the same mix? ; 

How do the unit compressive strengths obtained for the 
different mixes compare with the values given by Curve A of 
Fig. 3, page 18? 


JOB 70. PROPORTIONING CONCRETE BY THE USE OF THE TABLES 
OF THE 1924 JOINT COMMITTEE REPORT 


Object —To proportion a concrete mix, having a slump of 
6 in., to give a compressive strength of 2000 lb. per sq. in. at the 


LABORATORY METHODS 201 


age of 28 days by the use of the tables given in the 1924 Report 
of the Joint Committee on Standard Specifications for Concrete 
and Reinforced Concrete. (See Appendix 6.) 

Significance.-—These tables have been prepared to give suitable 
proportions of portland cement, fine and coarse aggregates to 
obtain a concrete of desired compressive strength at an age of 28 
days, when control tests (28-day compression tests on cylinders) 
are not to be made. 

References—Appendices 2, 3, 6, 7, and 8; Sec. I; and Jobs 
1, 6, and 10 to 13, inclusive. 

Materials—Portland cement and room-dry fine and coarse 
aggregates. The maximum size of the coarse aggregate should 
preferably be 114 in. Note the brand of the cement and the 
kinds of the aggregates. 

Apparatus.—Scales, measuring boxes, and tamping rods, as 
in Appendix 2 and Job 59; scales and sieves, as in Appendix 
3 and Job 60; slump test apparatus, as in Appendix 7; mixing 
platform, scales, shovels, trowels, and two or three 6- X 12-in. 
cylinder molds, as described in Appendix 8. If sufficient cylinder 
molds are available, it is better to make the cylinders in sets of 
three, instead of sets of two, as given in this and the following 
jobs. 

Method.—Determine the weight per cubic foot of each aggre- 
gate (if not previously determined) as in Job 59. 

Make sieve analyses of the aggregates as in Job 60. 

‘From the tables in Appendix 6, determine the required mix, 
having a slump of 6 in., to give a compressive strength of 2000 
Ib. per sq. in. at an age of 28 days, paying particular attention 
to the rules given in Appendix 6 for determining the limiting sizes 
of the aggregates. 

Compute the quantities of materials required to make two 6- X 
12-in. cylinders. 

Mix the concrete for these two cylinders, using enough water 
to give a slump of 6 in. when tested as directed in Appendix 7. 

Make the cylinders according to the directions given in Appen- 
dix 8. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test cylinders at an age of 28 days accord- 
ing to the methods given in Appendix 8. Observe the maximum 


202 CONCRETE PRACTICE 


(ultimate) load applied, and the manner of failure for each 
cylinder. 

If the unit weights and sieve analyses of these aggregates have 
been determined in preceding jobs, the values found may be 
used for this job. 

Report.—Compute the unit ultimate compressive strengths 
of the cylinders tested. Compute the water-cement ratio, and 
the number of gallons of water used per sack of cement. 

Questions ——Did the proportions selected give a greater or 
less unit ultimate compressive strength than 2000 Ib. per sq. in.? 

How does the average unit ultimate compressive strength 
obtained in this job compare with the unit strength given by 
Curve A of Fig. 3, page 18? 


JOB 71. PROPORTIONING CONCRETE BY THE WATER-CEMENT 
RATIO AND SLUMP TEST 


Object—To proportion a mix of concrete by the water-cement 
ratio and the slump test to obtain a mix having a slump of 6 
in. and a unit ultimate compressive strength of 2000 lb. per sq. 
in. at an age of 28 days. 

Significance—The water-cement ratio is the important ele- 
ment governing the compressive strength of a concrete mix. 
The strength may be said to vary inversely as the number of 
gallons of mixing water per sack of cement, irrespective of the 
amount of aggregate present, provided the concrete mix has a 
workable consistency. This consistency of the mix may be 
controlled by the slump test. 

References—Appendices 2, 7, and 8, Sec. I; Jobs 1, 7, and 10. 
to 13, inclusive. 

Materials—Portland cement and room-dry fine and coarse 
aggregates. The maximum size of the coarse aggregate should 
not be more than 144 in. Note the brand of cement and the 
kinds of aggregates. 

Apparatus—Slump test apparatus described in Appendix 
7 and scales, measuring boxes, mixing platform, shovels, trowels, 
two 6- X 12-in. cylinder molds, etc. for making concrete cylin- 
ders. If unit weights are to be found, the apparatus described 
in Appendix 2 will be needed. 


LABORATORY METHODS 203 


Method.—Determine the weights per cubic foot of the fine and 
coarse aggregates by the method in Appendix 2, if these weights 
are not available from previous jobs. 

Thoroughly mix the fine and coarse aggregates according to 
one of the following proportions. (a) If the coarse aggregate 
appears to be uniformly graded and has a suitable proportion 
of the smaller sizes of particles, use a 1:2 mix by volume (1 part of 
fine aggregate to 2 parts of coarse aggregate); or (b) If the coarse 
aggregate does not appear to be uniformly graded, or if a suitable 
proportion of the smaller sizes of particles are not present, use 
a 2:3 mix by volume (2 parts of fine aggregate to 3 parts of 
coarse aggregate). 

Obtain the weight per cubic foot of the mixed aggregate by 
the method given in Appendix 2. 

From Curve A of Fig. 3, page 18, 7/4 gal. of water per sack 
of cement should give a concrete having a unit ultimate compres- 
sive strength of 2000 lb. per sq. in. at an age of 28 days. Note 
the water-cement ratio. 

Ona water-tight mixing platform, mix thoroughly a half sack 
of cement (47 lb.), 334 gal. of water, and enough of the mixed 
ageregate, so that the resulting concrete will have a slump of 6 
in. when tested by the slump test. If care is taken in the adding 
of the mixed aggregate and water to the cement it is possible to 
obtain a mixture having a slump of 6 in. without much trouble. 

Norre.—In laboratory work, it is often preferable to weigh 
the materials. Cement weighs 94 lb. per cu. ft., water weighs 
62.355 lb. per cu. ft. or 8.35 lb. per gal., while the unit weights 
of the fine, coarse, and mixed aggregates may be found by the 
methods given in Appendix 2. 

Mold two (or three, if molds are available) 6- X 12-in. cylin- 
ders by the method given in Appendix 8. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test the cylinders at an age of 28 days. 
Note the maximum (ultimate) load applied, and manner of 
failure of each cylinder. 

Compute the ultimate unit compressive strength of each 
cylinder. 

Report.—Include in the report all essential data, computations, 
and results. 


204 CONCRETE PRACTICE 


Questions.—What were the proportions by volume of the 
cement to the mixed aggregate? What were the proportions 
by weight? 

What were the proportions by volume of cement, fine aggre- 
gate, and coarse aggregate? What were the corresponding pro- 
portions by weight? 

Was the average unit ultimate compressive strength more or 
less than 2000 Ib. per sq. in.? | 

How did the water-cement ratio in this job compare with the 
ratio of the preceding job? 

How did the proportions of the mix in this job compare with 
the proportions in the preceding job? 

How did the unit ultimate compressive strength of the concrete 
in this job compare with the strength obtained in the preceding 
job? 

Were the same aggregates used in both jobs? 

How did the unit ultimate compressive strength obtained in 
this job compare with the value given by Curve A of Fig. 3? 


JOB 72. PROPORTIONING CONCRETE BY THE WATER-CEMENT 
RATIO, SLUMP, AND FINENESS MODULUS OF AGGREGATE 


Object—To proportion a mix of concrete by the water-cement 
ratio, slump test, and fineness modulus of the aggregate, to obtain 
a mix having a slump of 6 to 7 in., and a unit ultimate compressive 
strength of 2000 lb. per sq. in. at an age of 28 days. 

Significance—The compressive strength of the mix is con- 
trolled by the water-cement ratio, the workability by the slump, 
and the economy by the grading of the mixed aggregate, as 
evidenced by the fineness modulus. 

References—Appendices 2, 3, 7, and 8; Sec. I; Jobs 1 and 8 to 
13, inclusive. 

Materials.—Portland cement and fine and coarse aggregates. 
The maximum size of the coarse aggregate should not be more 
than 1144 in. Note the brand of cement and the kinds of 
aggregates. 

Apparatus.—Apparatus for sieve analyses as described in 
Appendix 3, apparatus for determining unit weights as described 
in Appendix 2, slump test apparatus as described in Appendix 7, 


LABORATORY METHODS 205 


and scales, measuring boxes, mixing platform, shovels, trowels, 
two 6- X 12-in. cylinder molds, etc., for making concrete cylinders. 

Method.—If there is any doubt in regard to the quality of the 
fine aggregate, it should be tested for silt and organic impurities 
as described in Appendices 4 and 5. 

The relation between the compressive strength and water- 
cement ratio shown by Curve A of Fig. 3, page 18, will be 
assumed to apply on this job, because working conditions in the 
laboratory should be such that the proportioning can be accu- 
rately controlled. 

The detailed method of procedure given in Jobs 8 and 9 should 
be followed. 

The tests for slump and harshness should not be omitted. 

Using the proportions determined, compute quantities of 
materials required for two 6- X 12-in. cylinders. 

Mix the concrete and make the cylinders as directed in 
Appendix 8. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test the cylinders at an age of 28 days, 
according to the methods given in Appendix 8. Observe the max- 
imum (ultimate) load applied and the manner of failure for each 
cylinder. Compute the ultimate unit strength of each cylinder. 

Report.—Write a complete report for this job including all 
data and results. 

Questions.—Did the proportions selected give a greater or less 
ultimate compressive strength than 2000 lb. per sq. in.? 

Prepare a simple tabulation showing a comparison of the 
results obtained in Jobs, 70, 71, and 72 in regard to proportions, 
water-cement ratio, slump, and strength. Were the same aggre- 
gates used in all three jobs? 


JOB 73. EFFECT OF VARYING THE AMOUNT OF MIXING WATER IN 
A GIVEN MIX 


Object—To determine the effect of varying the amount of the 
mixing water on the consistency and compressive strength of a 
concrete mix. 

Significance-—It is advisable to use the smallest amount of 
mixing water that will give a workable mix, because the strength 
of a concrete mix varies inversely as the water-cement ratio. 


206 CONCRETE PRACTICE 


Increasing the quantity of mixing water in a mix of given pro- 
portions will increase the workability or slump, and will also 
decrease the compressive strength. 

References.—Appendices 7 and 8; Sec. I; Jobs 1 and 10 to 13, 
inclusive. 

Materials—Portland cement and room-dry fine and coarse 
aggregates. The maximum size of the coarse aggregate should 
not be more than 114 in. Note the brand of the cement and the © 
kinds of aggregates. 

Apparatus.—Scales, measuring boxes, mixing platform, shovels, 
trowels, eight 6- X 12-in. cylinder molds, and the slump test 
apparatus described in Appendix 7. 

Method.—Compute quantities of cement, fine and coarse 
aggregates, to make two cylinders using a 1:2:4 mix by volume. 

1. Make two cylinders using enough water to give a slump of 
about 1 in. 

2. Make two cylinders using 10 per cent more water than in 
(1). Observe the slump. 

3. Make two cylinders using 25 per cent more water than in 
(1). Observe the slump. 

4. Make two cylinders using 50 per cent more waten than in 
(1). Observe the slump. 

Observe how readily the water flushes to the surface when 
tamping the cylinders in the molds. Record the amount of 
water used in each batch. 

Follow the methods given in Appendices 7 and 8 when mixing, 
testing for slump, and molding the cylinders. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test all cylinders at an age of 28 days, 
observing the maximum (ultimate) load and manner of failure 
for each cylinder. 

Report.—Compute the water-cement ratio for each of the four 
mixes, and the unit ultimate compressive strength of each 
cylinder. Prepare a simple tabulation showing all essential 
data and results. 

Questions—Which consistency produced a concrete of the 
greatest strength? 

Was there any general relation between the weights of the 
individual cylinders and their compressive strengths? 


LABORATORY METHODS 207 


Was there any general relation between the water-cement 
ratios of the different batches and their compressive strengths? 

How did the unit compressive strengths obtained compare 
with the values given by Curve A of Fig. 3, page 18? 

How did the slumps obtained compare with the general 
statement made in regard to quantity of mixing water and slump 
in Job. 10, page 47? 


JOB 74. EFFECT OF VARYING THE FINENESS MODULUS OF THE 
AGGREGATE ON THE ECONOMY OF THE MIX 


Object—To determine the effect of varying the fineness modu- 
lus of the mixed aggregate on the economy of the mix. 

Significance—The amount of mixed aggregate, which may be 
added to a given quantity of cement and water to produce a mix 
with a certain slump, increases as the fineness modulus increases 
(and vice versa), as long as the mix is not too harsh. In other 
words, for a mix of a given strength and workability, the coarser 
the mixed aggregate, the greater the quantity or proportion of 
this mixed aggregate which may be used, and the greater the 
economy of the mix. 

References -—Appendices 2, 3, 7, 8; Sec. I; Jobs 1 and 8 to 13, 
inclusive. 

Materials—Portland cement and dry fine and coarse aggre- 
gates. The maximum size of the coarse aggregate should not be 
more than 114 in. Note brand of cement and kinds of aggregate. 

Apparatus—Apparatus for unit weights of aggregates, sieve 
analysis, and slump test, as described in Appendices 2, 3, and 7, 
respectively, and scales, measuring boxes, mixing platform, shov- 
els, trowels, six 6- X 12-in. cylinder molds, etc., for making 
concrete cylinders. 

Method.—Determine unit weights of the dry fine and coarse 
aggregates according to method given in Appendix 2. 

Make sieve analyses of the fine and coarse aggregates (accord- 
ing to the method given in Appendix 3), and compute their 
fineness moduli. 

Combine the fine and coarse aggregates in different proportions 
to give three mixed aggregates having fineness moduli of about 
5.2, 5.9, and 6.6, respectively. 


208 CONCRETE PRACTICE 


Using a water-cement ratio of 1 (7.50 gal. per sack of cement) 
and a slump of from 6 to 7 in., make three batches as follows: 

1. Using the mixed aggregate with a fineness modulus of about 
5.2. Note the proportion of mixed aggregate used, and then 
mold two cylinders. 

2. Using the mixed aggregate with a fineness modulus of about 
5.9. Note the proportion of mixed aggregate used, and then 
mold two cylinders. 

3. Using the mixed aggregate with a fineness modulus of about 
6.6. Note the proportion of mixed aggregate used, and then 
mold two cylinders. 

Follow the methods given in Appendices 7 and 8 when testing 
for slump and molding the cylinders. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test all cylinders at an age of 28 days, 
observing the maximum (ultimate) load and manner of failure for 
each cylinder. Compute the unit ultimate compressive strength 
of each cylinder. If the work has been carefully done, the 
individual strengths of the cylinders should be about the same. 

Report.—Prepare a simple tabulation showing all essential 
data and results. 

Questions.—Which value of the fineness modulus of mixed 
ageregate gave the most economical mix? 

What general conclusion may be drawn from the results of this 
job, in regard to the relation between the fineness modulus and 
the quantity of the mixed aggregate which may be added to a 
definite amount of cement and water to produce a certain slump? 

How did the unit compressive strengths found in this job 
compare with the value given by Curve A of Fig. 3, page 18? 

Did the unit compressive strength of any cylinder (or cylinders) 
vary greatly from the average of all? If so, was there any 
apparent reason for this variation? 


JOB 75. EFFECT OF VARYING THE FINENESS MODULUS OF THE 
AGGREGATE UPON THE SLUMP, AND UPON THE WATER- 
CEMENT RATIO REQUIRED FOR A GIVEN SLUMP 


Object—To determine the effect of varying the fineness modu- 
lus of the mixed aggregate: (a) upon the slump with the pro- 
portions of cement, water, and mixed aggregate remaining 


LABORATORY METHODS 209 


constant; and (b) upon the water-cement ratio required with the 
slump and proportions of cement and mixed ageregate remaining 
constant. 

Significance—With the proportions of cement, water, and 
mixed aggregate remaining the same, an increase in the fineness 
modulus (coarseness) of the mixed aggregate will increase the 
slump of the mix. With the slump and proportions of cement 
and mixed aggregate remaining the same, an increase in the 
fineness modulus (coarseness) of the mixed aggregate will decrease 
the amount of mixing water required to produce the given slump, 
and thus decrease the water-cement ratio and increase the 
strength of the mix, as long as the mix is not harsh. 

fveferences.—Appendices 2, 3, 7, 8; Sec. I; Jobs 1 and 8 to 13, 
inclusive. 

Materials.—Portland cement and dry fine and coarse aggre- 
gates. The maximum size of the coarse aggregate should not be 
more than 114 in. Note brand of cement and kind of aggregates. 

Apparatus.—Apparatus for unit weights, sieve analysis, and 
slump test as described in Appendices 2, 3 and 7, respectively, 
and scales, measuring boxes, mixing platform, shovels, trowels, 
six 6- X 12-in. cylinder molds, etc., for mixing concrete and 
making cylinders. 

Method.—Determine unit weights of the fine and coarse 
ageregates according to the method given in Appendix 2. 

Make sieve analyses (according to the method given in Appen- 
dix 3) of the fine and coarse aggregates, and compute their 
fineness moduli. 

Combine the fine and coarse aggregates in different proportions 
to give three mixed aggregates having fineness moduli of about 
5.2, 5.9 and 6.6, respectively. 

1. With a water-cement ratio of 1 (7.50 gal. of water per sack 
of cement), mix a batch of concrete, using enough of the mixed 
ageregate having a fineness modulus of about 5.2 to give a slump 
of about 3in. Note the proportion of this mixed aggregate used 
and the resulting slump of the mix. 

2. With the same water-cement ratio and the same proportions 
of mixed aggregate as in (1) mix a batch of concrete using the 
mixed aggregate, having a fineness modulus of about 5.9. Note 
the slump of the mix. 


210 CONCRETE PRACTICE 


3. With the same water-cement ratio and the same proportion 
of mixed aggregate as in (1), mix a batch of concrete using the 
mixed aggregate having a fineness modulus of about 6.6. Note 
the slump of the mix. 

4. With a water-cement ratio of 1 (7.50 gal. of water per sack 
of cement), mix a batch of concrete, using enough of the mixed 
ageregate having a fineness modulus of about 5.2 to give a slump 
of about 7 in. Note proportions of this mixed aggregate used. 
Make two cylinders from this batch of concrete. 

5. With the same proportions of cement and mixed aggregate 
as in (4) mix a batch of concrete, using the mixed aggregate 
having a fineness modulus of about 5.9 and just enough mixing 
water to give a slump of about 7 in. Note amount of mixing 
water used, and compute the water-cement ratio. Make two 
cylinders from this batch of concrete. 

6. With the same proportions of cement and mixed aggregate 
as in (4) mix a batch of concrete, using the mixed aggregate 
having a fineness modulus of about 6.6 and just enough mixing 
water to give a slump of about 7 in. Note amount of mixing 
water used and compute the water-cement ratio. Make two 
cylinders from this batch of concrete. 

Follow the methods given in Appendices 7 and 8 when testing 
for slump and molding the cylinders. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test all cylinders at an age of 28 days, 
observing the maximum (ultimate) load and manner of failure of 
each cylinder. Compute the unit ultimate compressive strength 
of each cylinder. 

Report.—Prepare a simple tabulation showing all essential 
data and results obtained in regard to the effect of varying the 
fineness modulus upon the slump. 

Prepare a similar tabulation, showing all essential data and 
results obtained in regard to the effect of varying the fineness 
modulus upon the amount of mixing water required for a given 
slump. 

Questions—From the results obtained, what general conclu- 
sions may be drawn in regard to the effect of varying the fineness 
modulus upon the slump when the water-cement ratio and pro- 
portion of mixed aggregate remain constant? 


LABORATORY METHODS 211 


From the results obtained, what general conclusions may be 
drawn in regard to the effect of varying the fineness modulus 
upon the amount of mixing water required for producing a 
given slump, when the proportions of cement and mixed aggre- 
gate remain constant? Upon the water-cement ratio of a mix 
when the slump and proportions of cement and mixed aggregate 
remain constant? Upon the strength of a mix when the 
slump and proportions of cement and mixed aggregates remain 
constant? 


JOB 76. EFFECT OF AGE ON THE COMPRESSIVE STRENGTH OF 
CONCRETE 


Object—To observe the effect of age on the compressive 
strength of concrete. 

Signi ficance.—In general, the compressive strength of concrete 
increases with age, the rate of increase in strength becoming less 
as the concrete becomes older. 

References.—Appendices 7 and 8; Sec. I; Jobs 1 and 10 to 13, 
inclusive. 

Materials—Portland cement and room-dry fine and coarse 
aggregates. The maximum size of the coarse aggregate should 
not be more than 114 in. Note the brand of the cement and the 
kinds of the aggregates. 

Apparatus.—Scales, measuring boxes, mixing platform, shovels, 
trowels, six 6- X 12-in. cylinder molds, and slump test apparatus 
as described in Appendix 7. 

Method.—Compute the quantities of materials required for 
the six cylinders using a 1:2:4 mix by volume. 

Mix the concrete using enough water to give a slump of about 
6 in., as shown by the slump test. Compute the water cement 
ratio. Follow methods given in Appendix 8 for making and 
molding the cylinders. 

Store the cylinders as directed in Appendix 8. 

Weigh, measure, and test two cylinders at an age of 7 days, 
another two at an age of 28 days, and the remaining two at an 
age of 60 or 90 days, as time permits. Note the maximum 
(ultimate) load applied to each cylinder, and compute its unit 
ultimate compression strength. 

Report.—Tabulate all essential data and results. 


212 CONCRETE PRACTICE 


Questions.—What general conclusions may be drawn regard- 
ing the effect of age on the compressive strength of concrete? 

Compare the unit compressive strength at 28 days with the 
value given by Curve A of Fig. 3, page 18. 

Using the average unit compressive strength at 7 days, find 
the probable unit compressive strength at 28 days from the 
curve of Fig. 5, page 21. 

How does the probable unit compressive strength at 28 days, 
found from the curve, compare with the unit compressive 
strength found in the 28-day tests? 


JOB 77. TESTS REQUIRED FOR CONCRETE MATERIALS 


This article is intended to be a general summary of the tests 
required of concrete materials. References are given to the 
jobs in which more complete information may be obtained. 

Before the concrete materials to be used on any job are tested, 
representative samples must be secured of each of the materials. 
Appendix 1, Sec. I, and Jobs 52 and 58 contain information in 
regard to the sampling of materials. 

For information regarding tests on portland cement, refer to 
Sec. I, Jobs 52 to 57, inclusive, and Appendix 1. The tests 
usually required of portland cement are: normal consistency of 
neat cement paste; soundness; time of set; tensile strength of 
standard sand mortar; and fineness. Tests rarely called for are: 
specific gravity; and chemical tests. 

On small and medium-sized jobs, most of the fine aggregate is 
used without any preliminary testing, though tests are being 
required more frequently on sands used for concrete on large 
jobs. Appendices 2 to 5 inclusive, Sec. I, and Jobs 58 te 65, 
inclusive, give considerable information in regard to the testing 
of fine aggregates. Tests that may be required are: weight per 
cubic foot; sieve analysis; silt; colorimetric test; bulking effect 
of water; percentage of moisture present; percentage of voids; 
and tension and compression tests of mortars made with a port- 
land cement of known quality, and the fine aggregate in question. 

Coarse aggregates are rarely tested when used on compara- 
tively small and unimportant concrete work. On many large 
jobs, the coarse aggregates are now tested to determine their 
suitability for concrete work. Further information relating to 


LABORATORY METHODS 213 


the testing of coarse aggregates is given in Appendices 2 and 3, 
Sec. I, and in Jobs 58 to 65, inclusive. Tests that are frequently 
asked for are: weight per cubic foot; sieve analysis; silt; percent- 
age of voids; and compression tests on concretes made with 
portland cement and fine aggregate of known quality, and the 
coarse aggregate in question. 

Water is rarely tested before using it for concrete purposes. 
If the water is suitable for drinking purposes, it is usually suitable 
for concrete mixes. Water that is not suitable for drinking pur- 
poses should be regarded with suspicion. Section I gives further 
information. 

Compression and tension tests are the ones usually required on’ 
portland cement mortars. Section I and Jobs 66 and 67 give 
information regarding the strength of mortars. 

Appendices 7, 8, and 9, Sec. I, and Jobs 1 to 14, inclusive, and 
68 to 76, inclusive, give much information in regard to the pro- 
portioning, mixing, molding, curing, and testing of concrete. 
Slump tests for consistency and compression tests are often 
required, while cross-bending and yield tests are rarely called for. 

Compression and absorption tests are usually required of 
concrete block and brick. Cross-bending tests are sometimes 
asked for. References for the requirements of concrete block 
and brick are Appendices 11 and 12, and Job 31. 

Questions.—Name the tests commonly required for each of the 
following: portland cement, sand, crushed stone or gravel, port- 
land cement mortars, portland cement concretes, and concrete 
brick and block. 


JOB 78. TESTING MACHINES USED IN TESTING CONCRETE AND 
CONCRETE MATERIALS 


Testing machines (other than the Vicat apparatus, Gillmore 
needles, briquette molds, etc., described in Appendix 1), used for 
testing portland cement and cement mortars, are briquette testing 
machines for tensile tests, and hydraulic compression or universal 
testing machines for compression tests. 

In the automatic briquette testing machine, the load is applied 
at a uniform rate (usually 600 lb. per min.) by shot flowing from 
a hanging bucket or receptacle in the machine. ‘There are many 
devices for regulating the flow of shot and applying the load. 


214 CONCRETE PRACTICE 


The machine is so constructed that the flow of shot is automati- 
cally stopped when the briquette breaks. The operation of the 


Fia. 77.—Automatic cement briquette testing machines. 


ordinary shot machine is as follows: See that beam balances with 
no load, place briquette in grips, tighten grips, start flow of shot, 


LABORATORY METHODS 215 


keep beam balanced by turning hand crank, observe and record 
breaking load when briquette breaks. The capacities of the 
automatic briquette testing machines are usually 1000 lb., though 
2000-lb. machines may be purchased. 

A hydraulic compression machine of from 50,000- to 200,000-Ib. 
capacity is useful for crushing mortar and concrete specimens 
where the ultimate strength is desired. Most of these machines 


Fig. 78.— Hydraulic compression testing machine. 


consist of a strong frame with an oil cylinder, in which oil is 
pumped by a hand or power pump. In operating the machine, 
the specimen is placed squarely in the center of the lower bearing 
block, the upper bearing block is brought down to the top of the 
specimen and tightened by means of the hand wheel at the top of 
the machine, the load is applied by pumping oil into the cylinder, 
and the load (represented by oil pressure) is read by means of the 
oil-pressure gages. One of the bearing blocks (preferably the 
upper) should be a spherical block. When the specimen is 


216 CONCRETE PRACTICE 


accurately centered in the machine, the spherical joint of this 
block helps to correct any slight lack of parallelism in the upper 
and lower surfaces of the specimen. 

The most common type of testing machine is the universal 
testing machine. The essential parts of this machine are a 
weighing platform for supporting the specimen, levers, a scale 


Fic. 79.—Universal testing machine. 


beam for measuring the load, and a pulling head connected to a 
gear system for applying the load. The weighing platform, 
levers, and scale beam are somewhat like those of an ordinary 
weighing scale. ‘The load is applied by means of a pulling head 
and screws (usually two, three, or four in number) operated by a 
set of gears attached to a motor or line belt. This pulling head 
can be operated at several different speeds. The load is always 
applied by a downward movement of the pulling head. Usual 


LABORATORY METHODS 217 


capacities of universal machines used in laboratories vary from 
50,000 to 200,000 Ib. 

In making compression tests (as of mortar or concrete speci- 
mens), a bearing plate is attached to the under side of the pulling 
head, and another bearing plate placed in the center of the 
weighing table. One of these bearing plates 
should have a spherical joint to care for a 
possible slight lack of parallelism in the 
upper and lower surfaces of the specimen. 
The specimen is placed on the lower bear- 
ing block, so that the vertical axis of the 
specimen and block are in the same line. 
The pulling head is then lowered until it is 
just in contact with the top of the specimen. 
The load is applied by moving the pulling 
head slowly downward, and the amount of 
the load is measured by moving the poise 
on the scale beam and keeping this beam 
balanced. 

A spherical bearing block is a necessary Lo 
adjunct for making compression tests. F1e.80.—Spherical bear- 
The spherical joint permits the part of the antes 
bearing block in contact with the specimen to move and eet 
itself to the test conditions. 

Questions.—Briefly describe the operation of an automatic 
cement briquette testing machine shown in the figure accompany- 
ing this job. 

Why should a spherical bearing block be used in a compression 
test? 

Briefly describe the operation of a universal testing machine 
when making a compression test. 


SECTION VI 
FIELD WORK 


INSPECTION OF CONCRETE WORK 


It is the duty of the inspector on concrete work to see that the 
contractor provides the materials called for, and does the work in 
accordance with the specifications and plans. Any deviations 
from the specifications and plans should be reported to his 
superior (engineer, architect, or owner, as the case may be). The 
inspector should be reasonable in his relations with the contractor, 
and should, as far as he is able, endeavor to see that the contrac- 
tor and owner both get a “‘square deal.’”’ The inspector should 
not be too rigid and arbitrary in requiring the contractor to con- 
form exactly to the plans and specifications, neither should the 
inspector permit any material deviation, however slight, from the 
requirements that would materially injure the work. A good 
inspector, who understands his work, soon wins the confidence 
and respect of a good contractor. A good inspector can often do 
much to aid the progress of the work, and at the same time to 
secure a good, satisfactory, workmanlike job. 

If the contractor and his workmen know how, and try, to do 
good work, the inspector’s job is an easy one. If the contractor 
and his men know how, but appear unwilling, to do good work, 
care, firmness, and continued vigilance are required of the 
inspector. When the contractor and his men do not appear to 
know how to do good work, the inspector must be firm and tact- 
ful, and endeavor to teach the workmen the correct methods for 
securing good results. If the inspector does not know his work, 
or if he is tactless, overbearing, and overcritical, he may cause 
considerable trouble and expense, both for the owner and a good 
contractor. A dishonest contractor will often take advantage of 
a lax and ignorant inspector. 

The duties of an inspector on concrete work may be summarized 
as follows: 

218 


FIELD WORK 219 


1. Excavation.—The inspector should observe if the earth has 
been excavated to the depths and dimensions called for. In case 
of backfill, he should see that the earth is properly placed and 
tamped. 

2. Materials—No materials should be used until they have 
been inspected and approved as to kind, quality, sizes, ete. 
When required, representative samples should be collected 
for testing. 

3. Forms.—The inspector must require that the forms be made 
and erected according to the requirements of the specifications 
and plans. He should check the dimensions inside of the 
column and beam forms. He should see that the forms are clean 
and properly wetted or oiled before the concrete is poured. He 
should require that all debris be removed from the inside of the 
forms, and that all opénings for removing debris be properly 
closed before pouring concrete. | 

4. Reinforcing Steel— When the steel is placed in the forms, 
the inspector should check sizes, bends, and spacing of rods. 
He should see that chairs and other steel supports and spacers 
are properly and securely placed, and that all ties are correctly 
made. In columns, the vertical rods must be securely tied to 
the spirals. 

5. Mixing Concrete——The mixing machinery must be clean 
and in good working order. No concrete should be mixed unless 
the inspector is on the job. He must see that the materials are 
charged to the mixer in the correct proportions (especially 
cement); that the correct amount of mixing water is used to give 
the consistency (and strength) called for; and that the concrete 
is thoroughly mixed before being discharged from the mixer. 
The mixing and transporting machinery must be washed and 
cleaned at the end of the run or of the day’s work. 

6. Placing Concrete-—The concrete should be taken from the 
mixer and placed in the forms before initial set has occurred. 
On the way from the mixer to the forms, the inspector should 
observe if the mix appears to have the right consistency and 
uniformity, and if there is any segregation of the materials. The 
inspector should note if the mix is carefully placed in the forms, 
and spaded and tamped to give a good dense concrete, free from 
air pockets, and with a smooth surface next to the forms. The 


220 CONCRETE PRACTICE 


inspector must be careful to see that new concrete is carefully 
bonded to old concrete, according to the directions given. 

7. Curing of Concrete-—The inspector should observe if the 
curing conditions are such as to give satisfactory results, and that 
the specifications are carefully followed in this respect. 

8. Removal of Forms—The inspector must see that the forms 
are removed at the correct time and in the proper order. The 
workmen should be careful not to chip, spall, or otherwise injure 
the concrete surfaces. 

9. Surface Finish—The inspector must note if all fins and 
projections are removed, and that all porous places are cut out 
and holes filled with suitable mortar or concrete. When a cer- 
tain surface finish is required, the nspe must see that this 
work is properly done. 

10. Cleaning Up.—After the work is completed and the struc- 
ture and premises cleaned up, the inspector should make a final 
inspection to see if the cleaning is properly done, and that the 
place is left in good shape. 

11. Reports.—The inspector should make all reports (usually 
daily ones) required of him in regard to his work. ‘The reports 
may deal with materials delivered and used, forms made and 
erected, steel bent and placed, concrete mixed and poured, forms 
removed, surface finished, etc., as may be required by his superior. 
In addition to the routine part of the report, the inspector should 
note and report the general progress of the work, and any unusual 
or important matters dealing with the job. A diary, carefully 
and conscientiously kept day by day in regard to the work, is 
a great help. 


SUPERVISION OF CONCRETE WORK 


The supervisor or foreman in charge of concrete work should 
try to obtain average quality and maximum quantity of work in 
the minimum amount of time. 

Foremanship, in general, consists of the ability to organize the 
gang, and to efficiently direct and supervise the work by properly 
dividing the work among the workers, educating the workers 
when necessary, coordinating the work of the different individuals, 
developing an esprit de corps or gang spirit, exercising tact and 
forbearance, and doing all that he can to secure satisfactory 
work at minimum cost. 


FIELD WORK 221 


Quality of concrete work depends upon good materials, proper 
tools and plant, correct methods of work, and good workmen. 
Good workmen in concrete are those who have sufficient educa- 
- tion, skill, aptitude, and experience to turn out satisfactory work 
in an efficient manner. ! 

Quantity of concrete work may be secured by use of good 
tools and methods, by correct location and arrangement of the 
plant, by proper organization of the gang, by the selection of good, 
efficient workers, by the development of gang speed, and by the 
avoidance of delays and idleness of the plant or of the workmen. 

To be efficient, the concrete plant for a small concrete job 
must be of the right size for the job. The mixer should be 
located as close to the forms as practicable. The pile of coarse 
ageregate should be closer to the mixer than the pile of fine 
ageregate. The cement for a day’s run (or at least for a half 
day’s run) should be piled close to the mixer so that the mixer 
tender or operator can also handle the cement. The plant should 
be so laid out that the total amount of labor per cubic yard of 
concrete will be a minimum. 

The concrete gang must be organized so that each man will be 
busy all the time. The time lost, due to delays and idleness, 
must be reduced to a minimum. Plant delays may be reduced 
considerably if the mixer operator keeps the mixer in good 
working order. Minor repairs, adjustments, greasing, etc. should 
be made outside of regular working hours. Idleness may be 
reduced by providing just enough workers for each class of work. 
For example, if two men can shovel and measure aggregates for 
the mixer, it is useless to have three men for this part of the 
work. 

Motion and time studies are advantageous in determining the 
most efficient ways of doing certain kinds of work. The studies 
tend to show what motions are needed for a certain type of work 
and what motions are wasteful and unnecessary. After the 
proper method of doing the work has been found, the worker 
must be taught and trained to follow these methods until he does 
the work easily and efficiently. There is also a certain ‘‘knack,” 
or way of doing work, that some men acquire more quickly than 
others. For example, an experienced shoveler in mixing con- 
crete does not try to fill his shovel by a short stroke or a jab at the 


222 | CONCRETE PRACTICE 


pile, but slides his shovel on the mixing platform and fills it 
gradually and uniformly over a stroke of about 2 ft. 

A foreman or superintendent should try by every possible 
means to avoid accidents to the workmen or plant. Accidents 
either to workers or plant cause delays and increased costs. 
Workers must be cautioned in regard to the use of certain parts 
of the plant, such as scaffolds, runways, ladders, etc. Plant 
accidents may be reduced by careful inspection at fairly close 
intervals. Guards should be provided for gears, chains, shafts, 
flywheels, etc., whenever practical. 

The following are some of the principles for securing minimum 
costs of concrete work: 

1. The sum of all of the units of cost should be a minimum. 

2. The plant and men should be worked to capacity. 

3. Delays and idleness should be reduced. 

4. Plant and work should be arranged.and organized to make 
the labor a minimum. 

5. Low-priced men should be used for low-priced work, and 
skilled labor used only when required. 

6. Overhead and plant expenses should be reduced to a 
minimum. 

7. A gang spirit (idea of best company, best gang, best boss, 
best men in that class of work) should be developed. 

8. The most profitable part of the work should be done first. 

When investigating costs of concrete work it is well to express 
each cost item as a percentage of the whole. Any items which are 
exceeding the percentage values assigned to them should be 
studied as to the cause and possible remedy. When trying to 
reduce costs, it is usually better to study the larger items first. 
The most efficient work may not always mean the fastest work 
but it does mean the work which was done for the least cost. 


The jobs in the Field Work Section are each divided into two 
parts—descriptive matter and field jobs or problems. In most 
instances, the descriptive matter is not intended to be complete 
but is intended to be supplementary to the material previously 
given in the text. While no back references are given, it is 
assumed that the preceding material has been studied and will 
be restudied when necessary. 


FIELD WORK 223 


- The field jobs or problems are frequently divided into two 
parts, (a) and (b). When so divided, the object of jobs (a) is to 
observe, record, and study the work done by others; and the 
object of jobs (b) is actually to do the work. Study, observation, 
and practical work are all necessary for a thorough understanding 
on concrete practice. 


JOB 79. CONCRETE BASEMENT—STAKING OUT 


The best and easiest way to stake out a basement is by the use 
of surveying instruments. When such instruments are not 


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Fig. 81.— Method of staking out a foundation. 


available, a 50- or 100-ft. steel tape may be used for measuring, 
and a carpenter’s level and straightedge for leveling. 

First a base line, marking one end or side of the basement, is 
established at the place where the proposed building is to be 
erected. Beginning at suitable points on this base line, lines for 
the other sides of the basement are laid out. 

In Fig. 81, line AB is the base line, and stakes A and B are 
driven at the corners of the basement. ‘Then the other lines 
AD, BC, and CD are located, and stakes sometimes placed at 
corners C and D. Nails may be driven in the tops of the stakes 


224 ; CONCRETE PRACTICE 


to locate the exact corners, or the inside edges of the stakes may 
be used to determine corners, and the batter boards omitted. 

Right angles may be laid out at any corner by the following 
method: Drive stake F (see Fig. 81) on line AB, and 6 ft. from 
stake A. Place nail in top of stake F exactly 6 ft. from nail in 
top of stake A. Drive stake # 8 ft. from stake A, and 10 ft. 
from stake F. Place nail in top of stake H exactly 8 ft. from nail 
in stake A, and exactly 10 ft. from stake F. Angle HAF is a 
right angle. Measure line AD (line AE prolonged), and locate 
point D. In like manner, lay off BC at right angles to AB, and 
locate point C. Measure BC for check. 

For a final check, measure the diagonals AC and BD. ‘These 
two diagonals should be exactly of the same length if the points 
A, B, C, and D form a perfect square or rectangle. If the lengths 
of the two diagonals are not exactly equal, move points C and D 
a little, and check distances again. Repeat process until the 
corners A, B, C, and D are located correctly. 

Erect batter boards 2 or 3 ft. from each corner, as shown in 
Fig. 81. The horizontal boards are often set level with the top 
of the proposed foundation wall, or a certain definite distance 
above or below. Suppose that the horizontal boards are placed 
at corner A first, and made level by use of the carpenter’s level. — 
Then the batter boards at corners B and D may be placed, and 
the elevations of the horizontal boards found by sighting along 
boards G and H, or by sighting along a leveled straightedge 
fastened to one of these boards. The elevations of the horizontal 
batter boards at C must be checked by sights from both B and D, 
and errors corrected. | 

Strings may be stretched vertically over the corner stakes A, 
B, C, and D by use of a plumb bob. Notches or nails are placed 
in the batter boards where the strings are fastened to mark the 
correct places in case the strings should be broken or removed. 

After having located the basement corners and lines, it is 
comparatively easy to locate any piers, posts, columns, or other 
supports for the building, either inside or outside of the building 
line as the case may be. 


Problems.—Stake out a building foundation for a basement 24 X 32 ft. 
in size, setting corner stakes, batter boards and strings, assuming that the 
top of the foundation wall at point A is to be 2 ft. above the surface of 


FIELD WORK 225 


the ground. Be sure that diagonals AC and BD check. Correct length 
of each diagonal in this job is 40 ft. Materials needed will be six stakes, 
twelve posts, eight boards, about fifty nails, a ball of heavy twine, a plumb 
bob, a good carpenter’s level, a 50 or 100 ft. metallic tape, a straightedge, 
a hammer, and an axe. 

Notre.—Other dimensions for the basement may be selected, if desired. 


JOB 80. CONCRETE BASEMENT—ESTIMATING 


The estimate for a concrete basement will be divided into five 

parts: 

. Staking out. 

. Excavation. 

. Forming. 

. Concreting. 

. Removal of forms. 

The method of staking out a basement was explained in the 
preceding job, and a list of materials given for staking out a 
simple rectangular basement. If old lumber is used, the cost of 
materials will be small. The labor required for staking out a 
simple basement will usually vary from 1 to 4 hr. for two or three 
men, depending on conditions. 

The volume of earth to be removed in excavations will be equal 
_to the area of the basement times the average depth of the bottom 
of the basement below the ground surface. When the ground 
surface is a plane surface (either level or inclined), it is compara- 
tively easy to find this average depth. If the ground surface is 
rolling or uneven, the basement area may be divided into several 
small areas (from 25 to 100 sq. ft., for example), and the average 
depth for each area approximately determined. Then the 
- volumes due to each area times its depth are computed and 
summed up to obtain the total. 

For a small basement where the dirt is to be used for grading 
around the place, the dirt may be removed by two men with a 
team and a scraper, and a shoveler or two. When the dirt is 
to be hauled away, it is usually shoveled directly into wagons 
or trucks. On comparatively large jobs, steam shovels and drag- 
line scrapers may be used. Plows or picks may be used for 
loosening the dirt. 

The form lumber for basement walls may be either 1-in. ship- 
lap or 1-in. boards, about 6 to 10 in. wide, and planed on one side. 


or Wd 


226 CONCRETE PRACTICE 


If the outer dirt walls of the basement are firm and smooth, they 
will serve as outer forms. For braces and struts and shores, 2 
< 4’s are commonly used. On many jobs, the form lumber for 
the basement is carefully salvaged and used for rough lumber in 


ii 


Fig. 82.—Method of computing excavation. 


the building. Planks are usually provided for constructing run- 
ways for the concreting gang. For ordinary walls, the vertical 
struts or cleats may be spaced about 2 ft. on centers. A net- 
work of cross-bracing from one wall to the opposite wall is often 
used instead of the bracing of wall forms shown in Figs, 26, 27, 


Fig. 83.—Small concrete batch mixer. 


28, 84, and 85. When the braces extend from the vertical 
struts to the ground, the lower side of these braces must be 
securely butted against stakes driven in the ground, and the 
upper ends fastened to the vertical struts. Cross-bracing from 
wall to opposite wall is to be preferred. 


FIELD WORK 227 


For an average basement wall, the proportions of the concrete 
mix usually vary from 1:2!4:5 to 1:4:7 when separate fine and 
coarse aggregates are used, and from 1:6 to 1:9 in the case of 
mixed aggregates (like bank run gravel). The thickness of the 
basement wall for a small basement may vary from 6 to 12 in., 
8 in. and 10 in. being common. 

In regard to concrete plant, a half-bag or a one-bag concrete 
mixer is commonly used. The crew required will vary from two 
or three men with a half-bag batch mixer to from four to six men 
with a one-bag batch mixer. 

In building work, the basement wall forms are removed in 
about 10 days to 3 weeks after placing the concrete, and the form 
lumber carefully salvaged, nails removed, boards cleaned, and 
piled for later use. The labor cost of form removal may be 
quite large, but is worth while as the salvaged lumber is used 
again. 

Problems.—Make a complete estimate of materials and labor for a 
basement with concrete walls. Size of basement is 24 X 32 ft., and walls 
are to be 8 in. thick and 7 ft. 6 in. high. Average depth to be excavated 
is 5 ft. 3 in. Concrete mix is to be 1 part of portland cement, measured by 
the sack, to 7 parts of bank run gravel, measured loose by volume as thrown 
into a measuring box or calibrated barrow or hopper. 

Notrr.—lIf an actual basement is to be staked out and excavated, use 
dimensions for that basement. 

1. Estimate materials and labor required for staking out. 

2. Estimate quantity of excavation (in cubic yards) and labor (man, 
team, scraper, and two helpers). 

3. Estimate form lumber in board feet, and labor in hours for forms. 
Assume outer dirt walls of basement to be firm and satisfactory as outer 
forms. 

4, Prepare a bill of material for the form lumber. 

5. Estimate quantities of cement and bank run gravel required. 

6. Estimate labor and plant (mixer, barrows, shovels, etc.) for con- 
creting, assuming a half-bag or a one-bag batch mixer for mixing, and 
barrows for placing the concrete. 

7, Estimate labor required for removing forms, removing nails, and clean- 


ing and piling form lumber. 
JOB 81. CONCRETE BASEMENT—EXCAVATION 


The excavation of small basements is frequently let for a 
lump sum or for a certain price per cubic yard. The lump sum 
contract is usually more satisfactory than day labor. 


228 CONCRETE PRACTICE 


When the dirt is to be used for grading on the lot, no dump 
wagons or trucks are needed. ‘The top soil is removed first by 
the scraper, and piled in one corner of the lot. This top soil is 
used for surfacing later on. A plow may be needed to loosen 
the soil from time to time. The scraper can remove about 80 
or 90 per cent of all the dirt, and the remainder must be shoveled. 
Shovelers are required to square the corners, smooth the walls 
af the dirt is comparatively stiff and firm), and to remove the 
last few cubic yards. 

When the dirt is to be hauled away, dump wagons and teams 
are commonly used. A wagon is placed in the basement area 
and loaded by a shovel gang. The number of men in the shovel 
gang may vary from two or three to six or eight, depending on 
the desired time of loading the wagon. An extra wagon or 
two should be provided, so that a wagon can be loaded while 
the teams are on the road. The first team arriving unhitches 
from its empty wagon and hitches on to the loaded wagon. As 
the basement gets deeper, an extra team (snatch team) is required 
to help ‘‘snatch”’ or pull the loaded wagon out of the basement. 
The number of shovelers, wagons, and teams required depends 
upon the length of haul and desired rate of progress. The whole 
gang should be organized so that neither shovelers nor teams will 
be idle during the working hours. More than one wagon may 
be loaded at a time if the size of the basement permits. 

Auto trucks are often not economical when they have to be 
loaded by shovelers. If the size of the excavation is large 
enough to warrant the use of a steam shovel, then auto trucks 
may be used. 

When boulders are found, the smaller ones may be carried or 
hauled out of the excavation. Larger boulders may be broken 
by sledges, drills and wedges, or explosives. 

Blasting is frequently necessary, when solid rock is encountered 
when excavating. ; 


Problems.—a. Observe the work of excavating a basement for a resi- 
dence, noting dimensions, quantities excavated, number of men, teams, 
wagons, scrapers, etc., on the job, and the work done by the different classes 
of labor, and the time spent on each class of work (plowing, scraping, shovel- 
ing, hauling, etc.). Compute the total hours of labor for both men and 
teams, and compare the results with reasonable estimates. 


FIELD WORK 229 


b. Excavate a basement, noting kind of earth, quantities excavated, 
number of men, teams, plows, scrapers, wagons, etc., used, and the cor- 


responding time. Compare actual labor hours required with the estimated 
hours. 


JOB 82. CONCRETE BASEMENT—FORMING 


Under similar conditions, the amount of forming lumber 
required for’a given basement will not vary greatly, but the 


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Fig. 84.—Foundation wall forms. 


amount of labor hours expended may vary greatly. For example, 
experienced, capable, and fast men can build interior wall forms 
for a 20- X 30-ft. basement, with a depth of about 7 ft. in about 
24 labor hr., while other workers may spend as much as 80 


230 CONCRETE PRACTICE 


labor hrs. on a similar job. Building the forms for each wall on 
the floor of the basement, and then erecting them, often saves 
considerable time. No more nails should be used than necessary. 

Pieces of lumber about 1 in. square, with a length equal to 
the thickness of the wall, make suitable spacers to keep the forms 
the required distance apart. These spacers may be removed 
as the concrete is placed. 

Wire ties are satisfactory for keeping the forms from spreading. 


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Fig. 85.—Foundation wall forms below grade. (The embankment serves as 
the outer form.) 


If the form carpenters are to set the runway planks for the 
concrete gang, care must be taken to secure the planks so that 
they will not move easily when the barrows and men pass over 
them. Care should be taken in regard to projecting the ends of 
planks beyond supports. Such a plank may tip up and cause a 
serious injury to a workman. 

Partially green lumber is usually satisfactory for form work, 
as dry lumber may swell, and too green or wet lumber may 
shrink. 


FIELD WORK 231 


Problems.—a. Inspect a job when basement wall forms are being con- 
structed, noting the amounts, kinds, and sizes of the form lumber used, 
together with the nails, spacers, and ties. Make a bill of material for the 
forms. Record the hours of labor required to construct the forms. 

b. If not previously done, make a bill of lumber and materials required 
for the wallforms for the basement previously excavated. Construct 
the wall forms for the basement, noting the materials used and labor hours 
expended. 


JOB 838. CONCRETE BASEMENT—CONCRETING 


Before starting the concreting work for the basement, the 
materials and plant needed should be on the job. The quanti- 
ties are not large, comparatively, and there should be no difficul- 
ties in regard to the storage space needed. 

The forms should be inspected to see if they are rigid and tight 
and well constructed. All rubbish should be removed from the 
interior of the forms. The surface of the forms with which the 
concrete will come in contact should be thoroughly wetted before 
concrete is poured. ‘The surfaces could be oiled, but most build- 
ers prefer a good wetting with water. 

The concrete plant should be examined to see if the mixer is 
clean and in good working order. Enough oil and gasoline should 
be on hand so that no delays will be caused by lack of them. The 
barrows, carts, shovels, and other tools to be used should be 
clean, and in good working order. The runways should be 
examined to see if they are well constructed and correctly placed 
for the work. 

The crew for a one-bag mixer will be approximately as follows: 

One man who acts as foreman, runs mixer, and adds cement 
and water to the mix. 

Two or three men to measure and load the aggregates in the 
hopper of the mixer. 

Two or three men to wheel and place concrete, depending on 
the capacity of the barrows or carts, and the size of the batch. 

One man to spade (and sometimes tamp) concrete in forms so 
as to get smooth surfaces, to remove spreaders, place stop boards, 
etc., and help barrow men when necessary. 

In general, the size of the crew should be such that the plant 
will be used efficiently and all men will be busy. A _ half-bag 
mixer will require a crew of about four men for efficient work. 


232 CONCRETE PRACTICE 


Whenever possible, the pouring of the concrete basement 
walls should be finished in 1 day. If necessary to stop work for 
a day before the concreting is completed, the joints between the 
old and new concrete should preferably be made horizontal. On 
beginning work again, all laitance and dirt should be removed 
from the surface of the old concrete before the new concrete is 
deposited thereon. If several days should elapse before the 
concreting is resumed, laitance and dirt should be removed from 
the surface of the old concrete and this surface roughened. A 
rich, thin cement grout should be applied to the old surfaces 
before the new concrete is deposited. ‘The new concrete should 
be placed before the grout has attained initial set. 

When the forms are full, the tops of the walls should be leveled 
and smoothed off. 

At the end of the job, at the close of a day’s work, or at any 
time when the process of mixing and placing concrete is inter- 
rupted for 14 hr. or more, the mixer and barrows (and other 
tools with adhering concrete) should be cleaned and washed. 


Problems.—a. Inspect a job when concrete basement walls are being 
poured, noting the size or capacity of mixer, size of batch, time required 
for mixing and placing a batch, the number of men in the crew and the 
duties of each, the amount of concrete mixed and placed, the time required, 
and the general methods of conducting the work. 

b. Mix and place the concrete required to fill the forms constructed in 
Problem (b) of Job 82. Note organization and duties of workers, average 
size of batch, amount of concrete placed, required time of placing, and any 
other useful information pertaining to the work. 


JOB 84. CONCRETE BASEMENT—REMOVAL OF FORMS 


Basement wall forms should not be removed until the concrete 
has attained hard set, and has become strong enough to sustain 
its own weight and the loads that may soon be placed on it. The 
time required before the forms should be removed. will vary 
from a few days in very hot weather to several weeks in very 
cold weather. Before removing the forms, the concrete should 
be examined to see if it is hard and firm. 

The forms should be carefully removed, so that the lumber 
will not be broken or split, the concrete cracked, or the surfaces 
marred. Nails should be removed from the form lumber, the 
boards cleaned, and the lumber neatly piled for future use. 


FIELD WORK 233 


Fins and projections on the exposed concrete surface should 
be removed. Holes should be filled with a mortar of about the 
same proportions as that in the concrete. Spongy and porous 
places should be cut out, and the cavities filled with a concrete 
or mortar of the same proportions as that in the walls. 


Problems.—a. Inspect a job when the forms are being removed from 
some basement walls, noting the appearance of the concrete, the care and 
manner in which the forms are removed, and the form lumber cleaned and 
handled, the amount of forms removed (square feet of form surface), 
and the labor hours required, the patching (if needed) of the concrete 
surfaces, and any other items of importance. 

b. Remove forms from the basement walls of Problem (6b) of Job 88. 
Remove nails, clean and pile lumber, and patch concrete surfaces. Note 
amount of form surface removed, labor hours required, and labor and 
materials required for patching surfaces. 


JOB 85. CONCRETE SIDEWALKS—SPECIFICATIONS AND 
ESTIMATES 


The following are general specifications in a condensed form 
for one-course and two-course concrete sidewalks. These speci- 
fications are practically the same as those proposed by the 
Portland Cement Association. 


Cement.—Portland cement meeting the standard specifications for port- 
land cement (Appendix 1). 

Fine Aggregate.—Clean and well-graded natural sand or screenings, 
from a hard and tough crushed rock, gravel, or slag. All shall pass a No. 4 
sieve, and 95 per cent or more shall be retained on a No. 100 sieve. 

Coarse Aggregate.—Clean, hard, durable, uncoated pebbles, crushed 
stone, or blast furnace slag. All shall pass a 1-in. sieve and 95 per cent 
or more shall be retained on a No. 4 sieve. 

Water.—Shall be clean enough to drink. 

Joint Filler—Premolded strips of bituminous filled fiber or mineral 
aggregate, 14 in. thick, as wide as the thickness of the walk, and 2 ft. or 
more in length. 

Forms.—Shall be of lumber 2 in. thick, or of steel of equal strength. 
Flexible strips may be used on curves. All forms shall be rigidly held to 
line and grade by stakes or braces. 

Division Plates.—Shall be of 1<-in. steel, as wide as the depth of the walk, 
and as long as the width of the walk. 

Subgrade.—Shall be well drained and compacted to a firm surface with 
uniform bearing power. 

Drains.—When necessary, 4-in. concrete or clay tile drains should be 
laid to protect the walk from possible damage by frost action. 


234 CONCRETE PRACTICE 


Subbase.—On poorly drained soil or where tile drains are impractical, a 
5-in. subbase of cinders, gravel, or other porous material shall be used. 
This material shall be thoroughly tamped and drained to a street gutter or 
other outlet. 

Thickness and Proportions of One-course Walk.—The concrete shall 
be at least 4 in. thick in residence districts and 5 in. thick in business dis- 
tricts. The proportions of the mix by volume shall be 1: 214: 4 for residence 
districts, and 1:2:3 for business districts. 

Thickness and Proportions of Two-course Walk.—In residence districts, 
the base course shall be at least 414 in. thick of a1:3:5 mix by volume. In 
business districts the base course shall be O4 4 in. thick, of a 1:3:5 mix by 
volume. The top course shall be at least 34 in. thick, oot the proportions 
of the mix shall be 1 part cement to 2 parts ane aggregate by volume. 

Mixing.—Concrete shall be mixed until each particle of fine aggregate is 
coated with cement, and each particle of coarse aggregate is coated with 
mortar. A batch mixer is preferred. 

Consistency.—The least amount of water should be used that will give a 
workable mix. The fresh concrete should require tamping to bring the 
water to the surface. 

Placing and Finishing One-course Walk.—Concrete shall be placed 
immediately after mixing. It shall be tamped, struck off with a template, 
and then floated with a wood float until the surface has a true contour. 
Care shall be taken not to bring an excess of water and fine aggregate to 
the surface by overfinishing. 

Placing and Finishing Two-course Walk.—The base course shall be 
thoroughly compacted by tamping, and then struck off with a template, 
which shall leave the upper surface of the base course 34 in. below the 
finished surface. The top coat shall be placed within 45 min. after the base 
course is laid. The top course shall be struck off and finished with a wood 
float until the surface has a true contour. 

Curing.—The new concrete shall be protected Hs a canvas or burlap 
covering for a day, after which the concrete shall be kept wet for 7 days. 

Problems.—Prepare an estimate of the materials, labor, and plant 
required for 200 ft. of one-course, concrete sidewalk, 5 ft. wide, assuming 
the following: 

Residence district. 

Average depth of excavation is 8 in. 

Subbase shall be 5 in. of cinders, with no tile drains. 


Nortr.—Instructor may vary conditions of this problem to 
conform with requirements of the next two (b) problems. 


JOB 86. CONCRETE SIDEWALKS—LOCATION, GRADE, BASE, AND 
FORMS 

In residential sections, walks are usually placed along the 

property line and a strip of lawn or parking is left between the 

walk and the pavement. Walks in the interior of the lot may be 


FIELD WORK 235 


placed where desired, and, when carefully located, will add to, 
rather than detract from, the appearance of the property. It is 
usually better to curve walks around a fine tree, instead of remov- 
ing the tree. The minimum width of walk in residence districts 
should be about 5 ft. 

In business and industrial districts, the walks usually extend 
from the building line to the curb, in order to give the needed 
width. Stronger walks are needed in these districts. 

In general, it should be planned to have the surface of the 
finished walk level with, or a trifle above (about 1 in.), the sur- 
face of the ground. Also the grade line of the walk should be 
approximately parallel to that of the pavement. A little study 
in regard to the grade line and location of the walk is well worth 
while when after effects are considered, especially when cuts or 
fills are encountered. 

The slope of the walk for drainage should be about 14 in. to 
the foot. The direction of the slope wil! often be determined by 
the slope of the surrounding ground. ‘The slope may be to one 
side, to the other side, or to both sides, as desired. 

In preparing the subgrade, the ground should be excavated 
to the depth desired, and all grass, sod, sticks, roots, and other 
vegetable matter removed. The surface of the subgrade should 
be tamped and compacted until it has a uniform bearing power. 
All soft and spongy places should be dug out and replaced with 
good earth, solidly tamped. Places in the subgrade that are 
harder than the average should be loosened and then tamped, 
so as to have the same bearing power (or degree of compactness) 
as the remainder of the subgrade. 

Fills must be solidly compacted in about 6-in. layers. Muck, 
quicksand, sod, soft clay, spongy or perishable material should 
not be used. Fills should extend about 1 ft. beyond the edges of 
the walk to prevent undermining of the concrete during rains. 
When practical, it is well to allow the fill to settle for some time 
before the walk is constructed. 

Good drainage of the subgrade is essential. If the subgrade 
is naturally well drained, no drain tile or cinders are needed. If 
the subgrade is water soaked, the best remedy is drain tile placed 
about 1 ft. or so under the walk, and near the edge from which 
most of the water comes. In many instances, a subbase of a 


236 CONCRETE PRACTICE 


porous material (say a 5-in. layer of cinders) is advantageous. 
A. drain must be provided to carry away the water from this 
porous material, or it cannot serve its purpose. 

Sidewalk forms may be of wood or of metal. Straight forms 
should be of wood 2 in. thick, or of metal of equal strength. 
Flexible strips may be used for curves. Forms must be set true 
to line and grade, and securely held in place by stakes and braces. 
The top of the forms should correspond with the finished grade 
of the walk. 

After the side forms are placed, division lines should be marked 
on them at intervals to locate the position of the cross forms and 
to mark the dividing lines to be cut through by the groover. 
The intervals should not exceed 6 ft., and 5-ft. intervals are 
common in most localities. 

Metal cross forms have been found to be very satisfactory. 
These forms should be placed at the marked intervals, so as to be 
perpendicular to the walk surface and to separate the slabs. 

Construction joints are the separation planes between the 
slabs, and are formed by the removal of the metal cross forms. 
The edges of these joints should be slightly rounded. 

Expansion joints are placed at intervals of about 50 ft. in the 
walk, and between the walk and the curb, or a wall or a building. 
Expansion joints are usually 14 in. wide, except that a 1-in. joint 
should be provided between walks and curbs. The joint filler 
should preferably be a bituminous-filled fiber 14 in. thick as 
wide as the walk is thick, and as long as the walk is wide. 

Problems.—a. Inspect the preparation of the subbase and forms for a 
concrete sidewalk, noting the average depth of excavation, condition of 
surface of subgrade, drainage (tiles, cinders, etc.), width, length, and 
thickness of walk, kind of walk (one or two course), kind of forms, workman- 
ship in regard to placing of forms, provisions for cross forms and expansion 
joints, and labor expended for excavation, drainage, and forms. 

b. Excavate and construct subbase and forms for a concrete sidewalk, as 
directed by the instructor. Note the amount of excavation, drainage — 
provisions, amount and kind of forms, and labor required for excavation, 
drainage provisions, and forms. 


JOB 87. CONCRETE SIDEWALKS—CONCRETING, FINISHING, AND 
CURING 


Before starting concrete work, the forms and subbase should 
be inspected to see if they are correctly constructed, and the 


FIELD WORK 237 


Fia. 86.—Side forms are set, the subgrade Fic. 87.—Concrete is dumped onto the 
smoothed off and metal division plates subgrade by barrows or direct from mixer 
installed. bucket. 


Fig. 88.—The concrete is spaded against Fig. 89.—This wooden screed is worked 
the forms and then struck off with a screed back and forth, bringing enough mortar to 
or template. the top to make a smooth surface. 


Fig. 90.—A wood float or belt smooths Fig. 91.—After the surface is finished, the 
the surface and the edges are rounded with division plates are lifted out, the surface is 
an edging tool along the side forms and the protected with canvas and kept wet for a 
division plates. week. 


Figs. 86—91.—Construction of one-course concrete sidewalks. 


238 CONCRETE PRACTICE 


concrete plant examined to see if it is clean and in working order. 
The materials for the work should be available on the job, or at 
least enough of the materials for a day’s work. Shortly before 
starting concreting, the surfaces of the metal forms should be 
well oiled, while the wooden forms may be oiled or wetted. 

If a half-bag batch mixer is used, the concreting gang will 
probably consist of from two to four men, mixing and placing 
concrete, and one finisher. With a one-bag mixer, from four to 
seven men may be used for mixing and placing, and one finisher 
and one helper for finishing. Two-coat work requires more labor 
for mixing and placing than one-coat work does. 

Care should be taken, when measuring, to see that the materials 
are correctly measured. Placing materials in the mixer by 
shovelsful is not measuring. A bottomless measuring box should 
be used to measure the aggregates. Cement may be measured 
by the sack. Wheelbarrows may be used for measuring if their 
capacities are known, or if the inside of the barrow is marked to 
show the height to which the barrow is to be filled. 

A batch mixer should be used whenever possible, and the mix- 
ing continued for at least a full minute. The drum must be 
completely emptied, before receiving the next batch. If hand 
mixing is used, precautions must be taken to secure thorough 
mixing (see Job 13, page 51). 

In one-course work, the concrete is placed a little high in 
the forms, tamped, and then struck off by a template riding on the 
side forms. A heavy template will compress the concrete a little. 

In two-course work the base course is placed at about the 
height of the side forms, tamped, and struck off by a template 
leaving the concrete surface 34 in. below the top of the forms. 
The wearing course is placed soon after the base course (never 
more than 45 min. later), tamped, and struck off ready for the 
finisher. If the base course has commenced to harden before the 
top course is placed, the top course may crack and scale off. 

Concrete for each slab should be placed continuously, so that 
all parts of each slab will harden together. 

Whenever work must be stopped, as at the noon hour, or at 
the close of the day, it is best to stop work only at the end of a 
slab. 


FIELD WORK 


~ 


Fia. 92.—A base course of dry mix is tamped 
34 inch below the finished grade. 


Fic. 94.—After the striking-off process 
the surface is finished with a wood float and 
the edges tooled to a rounded corner. 


Fie. 96.—At regular intervals a dry sand 
joint is made in the _ base-course; the 
mortar top is grooved above this joint. 


. 


Fic. 93.—The 34-inch mortar top follows 
close after the tamping and is struck. off 
with a screed or template. 


Fig. 95.—When desired, a very smooth 
finish may be obtained by using a steel 
trowel. 


Fig. 97.—Edging tools are used, both 
along the forms and at the cross joints to 
give proper finish to the walk. 


Figs. 92—97.— Construction of two-course concrete sidewalks. 


240 CONCRETE PRACTICE 


Most concrete walk surfaces are now finished with a wood float, 
as a metal float makes a smooth slippery surface. After the 
concrete has been struck off, it should be smoothed with the float, 
high spots leveled off, low spots filled, and excess water worked 
to the edges of the side forms. ‘Too much troweling brings water 
to the surface, and causes a chalky surface. Float marks may 
be removed by brushing the surface with a calcimine brush dipped 
in water. If a rough surface is desired, this may be made by 
lifting the wood float vertically away from the surface. 

The edges of each slab next to the side forms and construction 
joints should be rounded to approximately a 14-in. radius with 

steel edging tools. 
' Figures 86 to 97, inclusive, give a good idea of the methods of 
finishing one- and two-course concrete walks. 

Special surfaces may be obtained by using different types of 
aggregates for the top surface, or by finishing the surface by 
different methods. 

When colored effects are desired, only mineral coloring matter 
should be used, so as not to reduce the strength of the concrete. 
The weight of the coloring matter should not be more than 8 per 
cent of the weight of the cement. The cement and coloring 
matter should first be mixed dry. A sample should be made 
first, to see if the proportions selected give the desired color effect. 
The following mineral colorings may be used to secure various 
colors: 


CGLOR CoLorina MATERIAL 
Pink to red Red iron oxide 
Browns Brown iron oxide 
Yellow to buff Tron hydroxide 
Gray to blue slate Carbon black or manganese dioxide 


White White cement, white sand, and white rock © 


Concrete hardens best when kept moist. Consequently, 
immediately after the surface of the walk is finished, the walk 
should be covered with canvas or burlap placed a little above, and 
not in contact with, the surface. This covering may be removed 
after a day or so, and the walk kept wet by sprinkling for a period 
of at least 7 days. 

After 1 week or 10 days, the side forms may be removed and 
earth tamped in the holes left by the forms. 


FIELD WORK 241 


Problems.—a. Inspect the concreting and finishing of a concrete sidewalk, 
noting the length, breadth, and thickness of the walk, whether one- or two- 
course work, proportions of mix, kind of plant, size of mixer, crew and their 
duties, the amount of concrete placed in cubic feet, and in square feet of walk 
surface, and the labor hours used. 

b. Concrete and finish the concrete sidewalk for which the subgrade and 
forms were constructed in Problem (b) of the preceding job (Job 86). Note 
the organization of the crew, the amount of concrete placed, and the labor 
required. Pay careful attention to the curing of the concrete. Remove 
forms after an interval of 1 week or 10 days. 


JOB 88. CONCRETE CURBS AND GUTTERS 


There are three classes of concrete curbs and gutters: (1) 
separate curb; (2) combined curb and gutter; and (3) integral 
curb and gutter. Separate concrete curbs are rarely made, 
because of the joint next to the curb, where the water may work 


pees filler 


Construction 
Jour 


apie seer Gane hole apy eg Ming 
fess Desde as Eee ee ae See 


Fia. 98.—Cross section of Fic. 99.—Cross section of Fie. 100.—Cross sec- 
integral curb and gutter. combined curband gutter. tion of separate curb. 


through to the subbase. Combined curbs and gutters are good, 
though there is a joint between the gutter and the pavement. 
The integral curb and gutter are constructed simultaneously 
with the concrete pavement, and without any joints between the 
pavement and curb and gutter. 

The face of a concrete curb should be sloping and the corners 
well rounded, because such a curb and gutter are more easily 
kept clean and also cause no damage to tires, rims, and wheels of 
motor cars, parked alongside the street. 

The construction of the integral curb and the combined curb 
and gutter is illustrated in Figs. 101 to 112, inclusive. Typical 
cross-sections are shown in Figs. 98,99, and 100. ‘The height and 
width of the curb and gutter vary in different localities and on 
different jobs. Metal form surfaces should be oiled, and wooden 
form surfaces may be oiled or thoroughly wetted shortly before 
concreting. 


242 CONCRETE PRACTICE 


Fia. 101.—Setting curb forms on Fiag. 102.— Building up integral curb 
returns. on returns. 


Fig. 103.—A simple form for integral Fig. 104.—F acing the curb after 
curb. forms are removed. 


Fia. 105.—Finishing with specially Fia. 106.—Giving final finish with 
shaped trowel. brush. 


Fias. 101-106.—Construction of integral curb. 


FIELD WORK 243 


Fie. 107.—Placing concrete in forms. Fig. 108.—Tamping concrete to ap- 
proximate contour. 


Fic. 109.—Striking off base course Fig. 110.—Finishing with curb 
and mortar facing. machine. 


Fig. 111.—Edging—note division Fia. 112.—Finishing with brush. 
plates. 


Fries. 107—-112.—Construction of combined curb and gutter. 


244 CONCRETE PRACTICE 


The following specifications are practically the same as those 
recommended by the Portland Cement Association: 


Condensed Specifications for Integral Curb 


Cement.—Portland cement meeting the standard specifications for 
portland cement (Appendix 1). 

Fine Aggregate.—Clean and well-graded natural sand or screenings from 
hard, tough, crushed rock, gravel or slag. All shall pass a No. 4 sieve, and 
95 per cent or more shall be retained on a No. 100 sieve. 

Coarse Aggregate.—Clean, hard, durable, uncoated pebbles, crushed 
stone, or blast furnace slag. ‘All shall pass a 114-in. sieve and 95 per cent or 
more shall be retained in a No. 4 sieve. 

W ater.—Shall be clean enough to drink. 

Joint Filler—Shall be premolded strips of bituminous filled fiber or 
mineral aggregate 14 inch thick, and of the actual section of the curb. 

Forms.—Shall be of lumber 2 in. thick or of steel of equal strength. 
Flexible strips may be used on curves. Shall be held in place with suitable 
clamps to prevent bulging. 

Subgrade.—Shall be well drained and compacted to a firm surface, with a 
uniform bearing power. 

Proportions.—Shall be 1 part cement, 2 parts of fine aggregate, and not 
more than 8 parts of coarse aggregate by ype or the same as are used for 
concrete pavement. 

Expansion Joints.—A 1-in. expansion joint shall be made at every. joint 
in the pavement, and should be in perfect alignment with the joint material. 
When curbs are molded to shape by use of forms, the joint in the curb shall 
be made with a tapered separator of oiled wood 44-in. thick at the top and 
cut to the exact section of the curb. The filler must effect a complete 
separation between adjacent sections of the curb. 

Mixing.—Concrete shall be mixed until each particle of fine aggregate is 
coated with cement and each particle of coarse aggregate is coated with 
mortar. A batch mixer is preferred. 

Consistency.—The least amount of water should be used that will give a 
workable mix. The fresh concrete should require tamping to bring the 
water to the surface. 

Placing.—Concrete shall be placed immediately after mixing. It shall 
be tamped and spaded until a coat of mortar is adjacent to the forms, so that 
no coarse aggregate will show when the forms are removed. 

Finishing.—Concrete shall be struck off flush with the top of the forms, 
and shall be given a true finish with a wood float anda brush. If stone pock- 
ets appear when forms are removed, they shall be filled with cement mortar 
and troweled. Corners and edges shall be rounded. 

Concrete shall be struck off and finished true to cross-section. Finish 
with a float or curb tool and brush. Round the corners and edges. Forms 
to remain in place at least 24 hr. 

Curing.—Finished concrete shall be kept wet for 7 days. 


FIELD WORK 245 


Problems.—a. Observe the construction of a concrete curb and gutter, 
and note details in regard to plant, materials, mix, forms, labor (organization 
and amount), and placing, finishing, and curing of concrete. 

b. Make a complete estimate of materials, forms, plant, and labor required 
for 100 ft. of combined curb and gutter, using cross-sectional dimensions 
selected by the instructor. Set forms, organize gang, and construct the 
100 ft. of combined curb and gutter. Record materials, labor, forms, and 
plant used. Compare actual quantities and results with those estimated. 


JOB 89. CONCRETE PAVEMENTS—DESIGN, SPECIFICATIONS, 
AND ESTIMATES 


A properly designed concrete pavement will be well located, 
well drained; will have a good firm foundation or subgrade of 
uniform supporting power; will be of ample width for the present 
and near future traffic; will have a section of the correct sectional 
dimensions for the kind of traffic and type of subgrade; will have 
well-constructed construction and expansion joints; and will 
be constructed of concrete of the most economical proportions 
and consistency. 

The location of a city pavement is almost invariably deter- 
mined in advance, and the location of a county highway nearly 
always. Relocation of highways and questions of grade, align- 
ment, curves, cut and fill, drainage, subgrade, design of sections, 
etc., should be left to the judgment of well-qualified engineers. 

Good drainage is very important, and often determines the 
“life” of the pavement. Well-constructed side ditches should 
be built to care for the surface drainage of highways and take the 
water away from the roadway, and thus keep the water out of the 
foundation. The bottom of the side ditches should preferably 
be at least 21% ft. below the center of the roadway, and the ditches 
should be of ample capacity. These ditches should be provided 
with outlets spaced not too far apart. Culverts should be used 
to carry the water from one side to the other under the roadway. 

Subdrainage is not needed in some instances, such as in fills 
and where the foundation soil is naturally porous and well drained. 
Drain tile are required where the subsoil is not well drained or is 
not porous (such as clay). The drain tile should not be less than 
4 in. in diameter, and should be provided with sufficient outlets 
to carry the water away from the foundation. Tile lines may be 
placed under the center of the roadway, under one edge, or under 


246 CONCRETE PRACTICE 


each of the edges, and at a proper depth and slope efficiently to 
drain the water away from the foundation. The slope of a tile 
drain should not be less than 6 in. in 100 ft. 

Most every highway has some cut and fill. Excavation usu- 
ally does not cause much trouble if careful attention is paid to 
line, grade, width, and drainage. Drainage, both surface and 
subsurface, in cuts is important. Fills should be carefully built 
up in horizontal layers of not over 1 ft. in thickness. Each layer 
should be well compacted before the next layer is applied. When 
time permits, an embankment should be allowed to settle before 
any paving surface is applied on top of it. Large rocks, sod, 
sticks, stumps, etc. must be kept out of the subgrade. 

The subgrade should be roughly made to approximately its 
final shape, and then trimmed, scarified, sprinkled (if not already 


wan eeterene eee ene Ok a 5 Si ey (7 20 / ae 
ke Gauge-6}"5td Metal Parting Strip... OF Mic mmeerse led pi banc ac ial cn ; S 
= TES ee ee ae ee erence Sat ane, oe ————[= 


2 Ce $ EN ~y 3 s Pet 
SECULDG Ni AR Gd PRET Ae OE OE Pe 

is A AWK YAY) A SRYNS YK SIS USLASULE WIV yg ee ent ee ee e i 
Teeny apa dN CPS. SUegtade | “MRI Ga opsh 
a Deformed Bars 4-0" Long, 3*1/"Ctrs." | : 

. es en .. Transverse Bar, 
Parting Strip Pin 1*3" Long- Pressed Steel Stake 
Section Area 11.68 sq.ft. 


Fig. 113.—Cross section of standard concrete pavement— Wisconsin Highway 
Commission. 


9 
iY 


3 
2 
e 


damp), and rolled until the surface is well and uniformly com- 
pacted and ceases to creep. Rollers, varying from 2 to 10 tons 
in weight, have been specified by different engineers for subgrade 
rolling. Soft spots should be dug out and replaced by good soil 
placed in 6-in. layers, and each layer well tamped and compacted. 
The contractor should be given extra compensation if required 
to excavate soft spots deeper than 2 ft. It may be advisable to 
place a 2-in. sand cushion on some soils such as clays. . A uniform 
degree of compactness and supporting power is desired of the 
subgrade. 

The roadway should be at least wide enough, so that two cars 
can easily pass when traveling at ordinary speeds. Widths of 16, 
18, or 20 ft. are common, and greater widths are provided in 
instances where the volume of traffic demands it. Shoulders 
should be usually provided along each side of the highway pave- 


FIELD WORK 247 


ment. The width of the shoulders will vary in different localities 
and places. 

The cross-section of a city concrete pavement may be of the 
same thickness throughout, or the edges may be a little thinner or 
thicker than the center, depending on the opinion of the engineer. 
The thickness should not be less than 5 in. at any place, and 
greater depths may be needed for certain kinds of soils and types 
of traffic. 

The cross-section of a concrete highway should be made 
thicker at the edges than at the center, due to the tendency of 


--Edge of Pavement Transverse Bar Stake 

ee ‘Round Smoot, Races aA a races Longitudinal Bar Stake--.->4 
Py Be atti he & \|_.Metal Parting Strip I 
~ Concrete Slab in Place Wid Stops at Joint 

‘t-Metal Pin I'-3"long 

2 Paraftined Pasteboard Tube-: 


: 2 - Std. Metal Parting Strip 
Plan View 
a ‘Paraftined Pasteboard Tube 2+3 es £ Round Smooth Bars4-0'Long, 
aes of Pavement ee a oe of ee a 


“arting STB 
subgrade-" 


4 SE 4 Toh loint Material - Nar more 
qaGn two pieces per joint. 
Cross Section View 


Fra. 114.—Transverse joint detail for standard concrete pavement— Wisconsin 
Highway Commission. 


heavy trucks to stay near the edge of the pavement. The thick- 
ness selected depends on the foundation, traffic, strength of 
concrete mix, and amount of reinforcement. At the present 
time, the minimum thicknesses commonly specified are 9 in. for 
the edges and 5 or 514 in. for the centers, with 2 ft. or more for 
the taper. The Wisconsin Highway ehfvcent an uses 9 in. at the 
edges and 614 in. at the center, with a taper extending 4 ft. back 
from the edge. ‘The Illinois Highway Commission uses a 9-in. 
edge with a center thickness of 6 in. for rural concrete highways, 
and a thickened edge and a 7-in. center for highways near large 
cities and population centers. Greater thicknesses may be 
required for very heavy traffic and weak and variable subgrades. 


248 CONCRETE PRACTICE 


There is no doubt but that steel reinforcement is beneficial in 
concrete pavements, but engineers differ in their opinions in 
regard to the economy of the use of the reinforcement. The 
question is not yet entirely settled whether it is advisable to use 
steel reinforcement and a thinner slab or to use a thicker slab and 
no reinforcement. Ordinary pavement reinforcement may be 
steel fabric or steel rods properly formed into mats with dimen- 
sions of steel, spacings, and weights as specified. ‘The amount of 
reinforcement may vary from 20 to 150 lb. per sq. yd. of pavement 
surface. Longitudinal parting strips are used in most concrete 
pavements 18 ft. or more in width, and dowel pins are provided 


+g Smooth Roviid Bar _, _-Circular Are , 

189° —-—— x 
SS PS PN Sets ait woot REE EE : 
eo Metal Joint" ‘©! Crowned subgrade “~ “7Tai* 


“4 Deformed Bar 


il vairaberdeatia sh eek ~ fy SOS ger ei eae a i = 
cree tage tere righ meets 

“ wi sCrowned Subgrade LSA 

‘3 Deformed Bar 

Fig. 115.—TIllinois concrete highway sections. 


in all transverse construction and expansion joints, so as to reduce 
and confine the cracking and to keep the edge of one section from 
rising above the edge of an adjacent section. Steel reinforcement 
is usually provided in concrete pavements where they pass over 
culverts or form approaches to bridges. 

Transverse expansion joints should be spaced from 30 to 50 
ft. apart, and should be about 1 in. wide. A bituminous-filled 
joint filler should be used, and not more than two pieces should 
be used in any one joint. Longitudinal expansion joints should 
be provided between the pavement and concrete curbs (unless 
integral curb and gutter is used), and other structures. When 
the pavement is over 25 ft. in width, a longitudinal joint is usu- 
ally provided in the center. Longitudinal parting strips are 
now commonly placed in the center of concrete highways. 
Dowels should be placed as shown in the plans. Dowels in the 


FIELD WORK 249 


parting strip and longitudinal parts are 14-in. square or 34-in. 
round rods, 4 ft. long, placed 3 or 4 ft. on centers. At transverse 
construction and expansion joints, the dowels are usually 34-in. 
round rods spaced about 4 ft. on centers. At transverse expan- 
sion joints, one end of each dowel is placed in a tube of paraf- 
fined or oiled paper to prevent this end from bonding with the 
concrete, and to permit expansion and contraction of the slab. 
Concrete pavement slabs often vary from 25 to 50 ft. in length 
and from 16 to 25 ft. in width. 

When concrete pavements form approaches to bridges, the 
pavement section is usually widened, thickened, and reinforced. 

On curves, the outer edge of the pavement is superelevated, 
and the width is widened (usually on the inside) to make travel 
safer. The amount of superelevation and widening varies in 
different localities. The free sight distance on a curve should 
be at least 150 ft., and many engineers prefer a minimum of 300 
ft. when practicable. 

Guard rails should be provided when the side slopes are so 
steep as to be dangerous, or when the highway passes over bridges 
and large culverts. These guard rails may be of several different 
styles. There are some patented forms of wire mesh on the 
market which make excellent guards, when properly placed and 
constructed. ‘These wire mesh guards are designed so as to 
be elastic and to ‘‘give”’ to some extent when an auto hits them, 
thus tending to reduce the amount of damage to the vehicle and 
injury to the passengers. 

The concrete materials should be inspected and tested to see 
if they comply with the specification requirements in each case 
before they are used in the concrete mixtures. 

The proportions of the concrete mix vary in different localities. 
Wisconsin uses practically a 1:2:4 mix by volume, while other 
mixes are 1:2:3, 1:2:314, ete. A 1:2:4 mix is about the leanest 
that should be used. It is often better to give a strength require- 
ment and proportion the materials accordingly. The least 
amount of water should be used that will give a workable mix. 
The slump of a concrete highway mix should be about 1 in. as 
determined by the standard slump test. In no case, should the 
amount of water exceed 614 gal. per sack of cement with the 
aggregates dry. If aggregates are not dry, the amount of water 


250 CONCRETE PRACTICE 


in them must be found and allowed for. This corresponds to a 
water-cement ratio of about 0.83 and should give a concrete 
having a unit 28-day compressive strength of from 2250 to 2750 
Ib. per sq. in. Some engineers specify the number of gallons 
of water per sack of cement that the contractor may use in the 
mix, and then let the contractor work out the grading of the 
aggregates to give the greatest yield and yet have a workable mix. 
In no case, should the amount of fine aggregate in a batch be less 
than half, or more than, the amount of coarse aggregate. 

Any method of proportioning may be used that will give satis- 
factory results. Common methods are: measuring cement by 
the sack, and sand and coarse aggregate dry in measuring boxes; 
cement by the sack, sand inundated in a tank, and coarse aggre- 
gate dry in measuring boxes; and cement by the sack, and sand 
and coarse aggregate dry by weight. If aggregates are wet, the 
amount of water contained must be found and allowance made. 
The bulking effect of water in sand must be considered if the 
sand is wet. Water may be weighed or measured by any positive 
automatic device which may be set and locked. 

The forms, plant layout, and mixing, placing, finishing, and 
curing of the concrete will be discussed in more detail in follow- 
ing jobs. 

The specifications for Portland Cement Concrete Pavement 
for Highways given in Appendix 13 are good, and should be 
studied in detail in connection with the jobs on concrete pavements. 

When preparing estimates for a concrete highway, the following 
items should be considered: 

Cut and fill. 

Culverts and bridge work. 

Preparing subgrade. 

Forms for pavement. 

Concreting plant—including mixer, water pipes, tools, finishing 
apparatus, canvas and burlap pavement covers, trucks or narrow- 
gage railway for hauling materials from source of supply to the 
mixer, unloading plant at railway station, steam rollers, scrapers, 
etc. 

Cement. 

Fine and coarse aggregate. 

Water. 


FIELD WORK . 251 


Steel reinforcement. 

Joint fillers. 

Material for aiding the curing of concrete such as calcium 
chloride, hay and straw, sand, ete. 

Shoulders for the pavement. 

Guard rails. 

Labor for all of the different construction items. 

While the materials and plant needed may be estimated fairly 
accurately, it is more difficult to secure a reliable labor estimate, 
because of variations in labor skill and incentive to work, gang 
organization and spirit, possible delays due to weather and 
breakdowns, etc. 

Likewise, it is difficult for the average person to estimate unit 
and total costs for similar reasons, though a contractor who knows 
his gang and their work can make a fairly close estimate. 


Problems.—a. Make an estimate of the materials required for the 
concrete for 1.50 miles of concrete highway, 20 ft. wide, using the Wisconsin 
Highway Standard Sections and a 1: 2:4 mix by volume, with expansion 
joints placed every 40 ft. 

If practicable, make a complete estimate from the plans and specifications 
of a portion of a concrete highway in the process of being constructed, and 
check the estimate with actual quantities used on the job. 

6b. Prepare an estimate for a portion of a concrete highway pavement 
according to information given by the instructor in regard to the location, 
length, and section. Include estimates for preparation of subgrade, forms, 
concrete materials, plant, and all labor involved. This pavement section 
should preferably be a small section, such as may be later constructed by the 
class. 


JOB 90. CONCRETE PAVEMENTS—SUBGRADE AND FORMS 


The subgrade should be prepared as described in the preceding 
job and in Appendix 13. The length of subgrade that should 
be prepared ahead of the concreting crew will vary, depending on 
the length of the pavement that the concrete gang can lay in a 
day. Enough subgrade for from 14 to 2 days concreting should 
be prepared in advance of the concrete gang. 

The forms used may be either of wood or metal, but good 
metal forms are to be preferred. The specifications in Appendix 


202 CONCRETE PRACTICE 


13 give the requirements for both wooden and metal forms and 
their setting. 


Fig. 116.—Setting metal forms for concrete highways. 


Problems.—a. Inspect the preparation of the subgrade and the setting of 
the forms on a concrete highway job, observing methods of compacting, 
wetting, and rolling subgrade, and kinds of forms, and methods of setting 
and aligning them. About what distance was the subgrade prepared and 
the forms set in advance of the concreting crew? 

b. Prepare the subgrade and set the forms for the section of concrete 
pavement to be constructed later by the students. If the concrete is not 
to be placed soon, the subgrade must be inspected, checked, and wet down 
again, just before the concrete is placed. The estimates for this section of 
pavement were prepared by the students in a previous job. 


JOB 91. CONCRETE PAVEMENTS—CONCRETE PLANT AND 
ORGANIZATION OF CREW 


It is practically impossible to state just what should be 
included in a concrete plant for a concrete highway job, and to 
give the correct organization of the crew, because each concrete 
highway job is a separate problem by itself and requires a partic- 


FIELD WORK 253 


ular solution. Factors affecting this solution are equipment 
available, time limit of job, probable weather conditions, location 
of material supplies, location of job, kind and amount of labor 
available, and capacity and ability of contractor and his foremen. 

In the following paragraphs, a description will be given of a 
plant layout, equipment used, and labor gang and organization. 
It should be noted that, while a certain plant layout and crew 
organization may give good results on a certain job, the same 
plant layout and crew organization might not work efficiently on 
other jobs, due to factors previously mentioned. 

Most highway engineers prefer a mixer on the job to a central 
mixing plant, though the central mixing plant has proved to be 
economical in some instances. The mixer should be a batch 


Water Supply Line 


EEE __ Steel Forms 


+t Q angi ran 

ib ee 5 4 PEAe 
Concrete Concrete 
covered with} cova with 


Final Belt 
Bridge 


Stee/ Forms 


| A Foreman 2 E Form Setters 2 | Strike-off Board Men 

| B Mixer Operator | F Water Boy | K Finisher 

| C Batch Operator 1 G Joint Man 2 L Finishers Helpers — 

| D Subgrader 2H Concrete Distributors 2 MLaborers to cover finished pavement 


Fig. 117.—Concrete paving plant layout with three-bag mixer. 


mixer with a boom and bucket delivery. The mixer engine may 
be steam, gasoline, or oil. Oil engines seem to be preferred at 
present. Electric motors may be used when there is a supply of 
electricity available on the job. ‘The larger and medium-sized 
mixers should be able to move slowly under their own power. 
Smaller mixers can be moved a short distance by workmen when 
necessary. The sizes of mixers commonly used are 2-, 3-, 4-, 5-, 
and 6-bag batch mixers, with the larger sizes preferred, especially 
on large jobs. 

The aggregates may be hauled to the job in advance of the 
work and placed on or along the side of the subgrade. This 
requires that the materials be handled again, usually by wheel- 
barrows. ‘The cement, of course, cannot be placed on the job 
much in advance of the mixer. A water-tight platform (raised 
a few inches off the ground) and some tarpaulin covers will be 
needed for the cement. 


254 CONCRETE PRACTICE 


The cement and aggregates may be hauled to the mixer in 
trucks or in industrial railway cars, and dumped into the mixer 
skip as needed. ‘The aggregates should be correctly proportioned 
for each batch at the loading plant, and each truck or car may 
hold one, two, or three batches, depending on the capacities of 
the mixer and of the truck or car. The proper amount of cement 
for each batch should be placed in bags on top of the aggregate 
for that batch. | 

Motor truck haulage of materials is suitable for jobs and 
plants of all sizes, while industrial railways are often uneconomi- 
cal, if used with smaller jobs. 

When the aggregates are hauled directly from the sand and 
gravel pits and stone crushers, the aggregate supply companies 
will usually have all bins and loading devices necessary. When, 
however, the contractor hauls his aggregates from a railway sid- 
ing, he will need machinery and appliances for unloading the cars 
and loading the trucks. When practical, the aggregates can be 
unloaded directly from the cars to trucks or bins. It is usually 
better to provide storage piles than pay demurrage charges. 
When the size of job warrants, bins should be provided for holding 
the aggregates and loading the trucks. Bins with weighing or 
measuring devices are needed when trucks are loaded by batches. 
A weather-tight cement storage shed capable of holding a car- 
load or more of cement is often essential. With batch loading, 
this cement shed should be located near the aggregate bins, so 
that the required sacks of cement can be placed on top of the 
ageregates for each batch. A truck turntable at the job is ahelp 
when batches are hauled by trucks. 

It is advisable to keep trucks, materials, etc., off of the pre- 
pared subgrade as much as possible. Any roughening or dis- 
turbance of the subgrade surface must be rectified before the 
concrete is placed. 


A typical organization for a 3-bag batch mixer is as follows: 


One foreman One joint man 

One mixer operator Two concrete distributers 

One batch operator Two strike-off board men 

One subgrader One finish foreman 

Two form setters Two finishers or helpers 

One water boy Two laborers to cover finished 
pavement 


EE —— 


FIELD WORK 290 


Enough trucks and drivers should be used to keep the mixer 
well supplied with materials. The number of trucks needed will 
depend on the size of mixer or batch, the size of trucks, and the 
length of haul. One truck turntable man will be needed if a 
turntable is used. 

If the cement and aggregates are piled on the job in advance, 
three or four cement handlers, five or six fine aggregate wheelers, 
and eight coarse aggregate wheelers are necessary. One or two 
trucks will be needed for hauling cement. 

If the pavement is to be reinforced, one or two men will be 
needed to place reinforcement. 

When the materials are unloaded at a railway siding, and 
batch haulage is used, one crane operator, one or two bin operators, 
one cement loader, two cement unloaders (from cars to shed), 
and possibly two shovelers will be needed. One foreman will be 
needed at the siding. When advisable, some laborers may be 
shifted from one kind of work to another. 

Compared with a 3-bag batch mixer, a 6-bag batch mixer will 
require about 50 per cent more laborers and about twice as many 
trucks. 

Problems.—a. Inspect a highway concreting plant in operation and 
write a report describing the plant layout and crew organization in detail. 

b. In regard to the section of concrete pavement to be built by the class, 
overhaul plant available and place it in good ‘working order, and determine 
the size of crew needed, crew organization, and duties of each laborer. 

c. Prepare a detailed estimate of the organization required for a 6-bag 
batch concrete mixer, giving the number of laborers of each class and their 
duties. Assume batch haulage with trucks having a capacity of approxi- 
mately 2 cu. yd. and an average length of haul of 3 miles from railway siding 


to job. How many trucks are needed? Plan the materials. plant at the 
railway siding, and list the number of workers required and their duties. 


JOB 92. CONCRETE PAVEMENTS—PROPORTIONING, MIXING, 
PLACING, AND FINISHING CONCRETE 


Just before starting the concreting, the subgrade should be 
rechecked to see if it conforms to the specifications, and any irregu- 
larities corrected. The subgrade should be moist, so-that it will 
not absorb water from the concrete. It is advisable to sprinkle 
the subgrade until it does not readily absorb any more water. 
When desired, the subgrade may be wet down from 12 to 36 hr., 
before placing the concrete. 


256 CONCRETE PRACTICE 


The reinforcement of the type, size, and weight shown on the 
plans prepared by the engineer should be placed as directed in 
the specifications (Appendix 13). Care must be taken to secure 
the reinforcement in its proper place, so that it will not readily 
be displaced when the concrete is poured. 

Any method of measuring the materials, including water, 
that will accurately give the required proportions is satisfactory. 
Aggregates should be dry, unless their water content is found 


Fic. 118.—Charging the mixer. 


and allowed for, or except when the sand is measured by the 
inundation method. The amount of water per sack of cement 
must be accurately controlled. 

The mixer should conform to the specifications in _ regard to 
type and operation. Some engineers require a net mixing time 
of 114 min. instead of 1 min., as usually specified. 

The mixed concrete should be deposited rapidly and uniformly 
over the subgrade. ‘Tamping, spading, and slicing is advisable 
to remove air from the concrete, and to compact it thoroughly 
and uniformly. 


FIELD WORK 257 


A mechanical tamper is sometimes used as in the Vibrolithic 
process. In this process, a set of duck boards of definite size, with 
spaces between them, is placed on the fresh concrete, and a gas 
or oil engine, with an unbalanced flywheel, is pulled back and 
forth across the boards. The unbalanced flywheel, when rota- 
ting, acts as a tamper and thoroughly compacts the concrete. 
More coarse aggregate should be added from time to time, so 
that there will not be an excess of mortar on the pavement 
surface. 


Fig. 119.—Spreading concrete on subgrade. 


The concrete pavement surface may be finished according to 
any one of the methods given in the specifications. Some engi- 
neers prefer to roll the fresh concrete across the pavement with a 
6-ft. wooden or metal roller after the concrete has been struck 
off, and before it has been belted. The roller should not weigh 
more than 50 Ib., should have a smooth surface, and should be 
from 8 to 12 in. in diameter. The roller should be built in two 
sections, so that these sections may be separated a little when 
a, joint is reached, and the concrete on both sides of the joint rolled 
in one operation. All portions of the concrete surface should have 
at least three separate rollings. 


258 CONCRETE PRACTICE 


In regard to the finishing of joints and edges, some engineers 
prefer a 3g-in. or a /4-in. radius instead of the 14-in. radius, speci- 
fied in the standard specifications. 


Fria. 120.—Construction of a concrete highway. 


Fig. 121.—Mechanical finishes. 


The finished surface should be such that it will conform to the 


required form of cross-section without a deviation of more than 


14 in. at any place. In regard to the longitudinal trueness of 


FIELD WORK 259 


the surface, a 10-ft. straightedge placed parallel to the center 
line of the pavement should not show a deviation of more than 
44 in. The pavement surface should be tested for trueness 
before the last finishing operation is begun, and concrete removed 
or added as needed to give the required smoothness .of surface. 
When concrete is added or removed at any point, the surface 
of this point must be completely refinished. 


Problems.—a. Inspect the mixing, placing, and finishing of a section of a 
concrete pavement or highway, noting kinds and proportions of materials, 
plant details, pavement cross-section, reinforcement, joints, etc., and the 
methods of mixing, placing, and finishing the concrete. Note the amount 
of pavement placed in a day’s run (square yards of surface and cubic yards of 
concrete), and compute the labor hours required per square yard of surface 
and per cubic yard of concrete. 

b. Wet down the subgrade and mix, place, and finish the section. of 
concrete pavement for which the subgrade and forms were prepared in the 
previous job. Compute labor hours required per square yard of pavement 
surface and per cubic yard of concrete. 


JOB 93. CONCRETE PAVEMENTS—CURING 


As the curing or hardening of concrete is not a ‘drying out’’ 
process, the concrete should be protected so that the moisture 
needed will not be evaporated. Concrete hardens best in the 
presence of moisture, hence the newly laid pavement should 
be covered or screened against the action of a hot sun or of a 
drying wind. 

The standard specifications for concrete highway pavements 
given in Appendix 13 describe the protection of the fresh concrete 
by burlap or canvas covers, wet earth covers, and sprinkling or 
ponding. To be efficient, the covering must be kept wet. 

Shrinkage cracks or “hair checks”’ are apt to form on the pave- 
ment surface during very hot and dry weather, due to the unequal 
shrinkage of the concrete and the exposed surface drying out a 
little. Working the pavement surface by tamping and belting 
until the hardening is fairly well advanced will help close 
shrinkage cracks, or help prevent such cracks from forming. 
Another method of preventing these shrinkage cracks is to cover 
the fresh concrete with burlap strips, and then keep the burlap 
moist, by spraying water through atomizing jets so as to keep a 
fine mist over it. 


260 CONCRETE PRACTICE 


When the concrete has hardened sufficiently, so that shrinkage 
cracks will not form, but is not yet hard enough to permit pond- 


Fig. 122.—Curing concrete pavement with burlap cover. 


Paid i Si 4 Py ~ 


Fig, 123.—Curing concrete pavement with earth cover. Placing the earth cover. 


ing or covering with earth, the pavement surface may be pro- 
tected by canvas covers attached to frames. These frames span 


ee 


FIELD WORK 261 


the pavement and keep the canvas a short distance above the 
concrete surface. Every other frame should have a strip of 


Fig. 124.—Curing concrete pavement with earth cover. Wetting earth cover. 


Fig. 125.—Curing concrete pavement by ponding. 


canvas to serve as a transverse partition across the pavement 
and thus prevent drafts along the surface. The canvas cover 
should be kept moist by spraying lightly with water. 


262 CONCRETE PRACTICE 


...When the concrete has hardened so that it may be covered with 
arth or ponded, the canvas-covered frames may be removed and 
the concrete surface protected for about 2 weeks by ponding or 
by an earth covering. Figures 122 to 126, inclusive, show various 
methods of protecting the newly laid concrete pavement. 

When it is practically impossible to protect the pavement 
surface by coverings or ponding, as in the case of some city 
streets, the fresh concrete surface may be kept wet by sprinkler 
heads arranged at suitable intervals, and connected by a hose to 
the city’s or contractor’s water supply. The sprinkler heads 


Fic, 126.—Curing concrete pavement with hay or straw cover, 


should be adjusted so that the water will fall on the concrete in 
the form of a fine spray or mist. 

Calcium chloride salt or crystals spread on the concrete surface 
(not less than 14 Ib. per sq. yd.) accelerates the hardening of the 
concrete, and tends to keep the surface from drying out too 
rapidly. The calcium chloride should not be applied until at 
least 24 hr. after the pavement is laid, and then only after the 
pavement has been kept thoroughly wet by sprinkling with water 
for the entire period, except the last hour just previous to the 
application of the calcium chloride. If rain falls within 2 hr. 
after the calcium chloride has been applied, an additional appli- 


FIELD WORK 263 


cation must be made. The calcium chloride should not be applied 
by shovels or brooms, but may be applied by a squeegee, or a 
suitable mechanical device giving a uniform distribution. 

Coatings of sodium silicate and other materials have been used 
in some instances, but laboratory tests have not shown these 
coatings to be superior to ponding or moist earth covers. 

In general, no such protective measures are necessary when the 
temperature is 50°F. or less. While concrete hardens less rapidly 
at low temperatures, there is but little evaporation of moisture 
from the concrete surfaces. 

Concrete pavements preferably should not be placed during 
freezing weather (35°F. or less). Article 70 of the specifications 
in Appendix 13 gives instructions for cold weather work. 

Before the highway is opened to traffic, shoulders should be 
constructed on both sides of the pavement. The material for 
shoulders should be of the kind specified, and should be placed, 
tamped, or rolled to conform with the requirements of the plans 
and specifications. 


Problems.—a. Inspect the curing of a concrete pavement, noting methods 
used in detail for protecting the concrete surfaces, time required, and approxi- 
mate labor needed. 

b. Using the method selected by the instructor, protect the surface of 
the pavement placed in previous jobs for a curing period of 2 weeks. 


JOB 94. CONCRETE SEPTIC TANKS 


Briefly, the principle on which a small sewage disposal system 
operates is that of bacterial decomposition (or rotting) due to 
the action of bacteria. There are two classes of these bacteria: 
aerobic bacteria which require the presence of oxygen (air); and 
anaerobic bacteria, which do not need oxygen (or air). Usually 
the small sewage disposal system is composed of a septic tank, 
which is comparatively tight, and in which anaerobic bacteria 
work, and a distributing system, which may be a dry well, or a 
system of drain tile, and in which aerobic bacteria can work. 

A concrete septic tank should be about 5 ft. deep, as experience 
has shown that a depth of about 4 ft. of liquid is essential, and of 
sufficient width and length to care for the average amount of 
sewage received in 1 day (about 50 gal. per person). Baffle plates 
should be placed close to the entrance and discharge pipes, or else 


264 CONCRETE PRACTICE 


the tank should have a central partition so as to lower the velocity 
of the liquid through the tank. Concrete baffle boards about 2 
in. thick are permanent. The length of the tank should be 


“ _-3 Bars 4"0¢.--, 


House grass RSH LDS 
ek | Chipped vent- 
ane —] 


—-_ 
4 a 
. ea ae 
WI 


>) 


a " 


me Bars, |2"0.c. |an eae 
both ways if 


Fia. 127.—Cross sections of single chamber septic tank and siphon chamber. 


approximately twice the breadth. The sewage may be dis- 
charged directly into the distributing system, or into a siphon 
chamber. The top of the septic tank should preferably be com- 


Fig. 128.—Forms for single chamber septic tank. 


posed of tightly laid concrete plank, which may be removed when 
the tank requires cleaning. Many authorities prefer the use of 
a siphon chamber, especially when tile drains are used to distrib- 
ute the sewage. The siphon causes a periodic discharge, which 


FIELD WORK 265 


nts SRN Te 
(pT 


IE REEY 


Nah 


8 
Ne beets @ Peace, 
of erase hr rae peri oe 
5 


Fie. 129.—Septic tank with siphon chamber. 


% Rods - #’ oc. 


Fig. 130.—California type of septic tank, 


266 CONCRETE PRACTICE 


tends to fill the drain tile for a time and to reduce the chance of 
clogging the tile near the septic tank. The use of a siphon is not 
so essential when a dry well is built. 

When drain tile are used to distribute the sewage, the tile may 
be arranged in two, four, or six lines and of sufficient length for 
the purpose. A longer system is required in a tight soil than in 
a porous one. The slope of the drain tile should be from 2 to 6 
in. per 100 ft. of length. The table which follows gives approxi- 
mate lengths of tile needed for tanks of various sizes and for differ- 
ent soils. Drain tile 4 in. in diameter is commonly used. The 
tile system should have an air vent, which is usually constructed 
near the septic tank and spihon chamber. 

A dry well makes a satisfactory distributing system when the 
well can be carried down to sand or gravel, or to rock crevices. 
The bottom of the dry well should be 5 ft. or more below the 
bottom of the septic tank, and the horizontal cross-sectional area 
of the dry well should be about four or five times that of the septic 
tank. The dry well may be walled up with stone or brick laid 
loose, and a concrete cover provided. ‘This cover preferably 
should not be lower than the top of the septic tank. ‘The cover 
should be provided with a suitable manhole and cover for cleaning 
purposes, and an air vent should extend from the top of the dry 
well to the ground surface. 

In most instances, the dirt walls of the excavation may be used 
for outer forms of the septic tank and inner forms of wood con- 
structed as in Fig. 128. The walls and bottom of the septic tank 
should be 5 or 6 in. thick, and should be reinforced with woven 
wire or with 14-inch round rods spaced about 12 in. on centers in 
both directions. The reinforcement should extend down the 
walls and across the bottom of the tank, forming a kind of steel 
basket. The concrete mix should be about 1:2:3 by volaIag: good 
materials being used. 

The cover of the septic tank should be made in the form of 
planks, as shown in Fig. 129. These concrete planks should be 
4 in. or more thick, and reinforced in the bottom with 14-inch 
round bars running lengthwise of the plank. The thickness of 
the plank and the amount of reinforcement will depend partly 
on the depth of dirt over the top of the tank. 


FIELD WORK ) 267 


Figure 131, and the following table, give the dimensions of 
septic tanks of different capacities. These dimensions are the 
ones recommended by the Portland Cement Association. When 
a siphon chamber is not required, the tank may be constructed 
according to dimensions, A, B, C, and F. For tanks having a 


VU 
Plan of tank with 
siphon. 
Cross section of tank with Cross section of 
siphon. single chamber 
tank. 


Fie. 1381.— Diagrams of septic tanks. 


capacity of 750 gal. or less, 3-in. siphons are suitable, and 4-in. 
siphons are required for the larger tanks. 


DIMENSIONS OF Septic TANKS 


Dimensions Suggested length of 
Maximum tile system 
number of | Capacity yi B C D E F 
persons in gallons Paes. 
served bi & i g e 8 ie g y g S Open Tight 
e S ® S 2 S 2 S ® g % | soil, feet | soil, feet 
les) Pel ee | Ble tl elie |] ee Be 
5 250 2 4|...| 6 Zed ale One L 150 250 
10 500 3 5| 41] 5 BY Ie cca) kobe al 300 500 
15 750 Selon son tLOn eS By Meter) PA es al 450 750 
20 1000 SMe A harsl 5) oy KOM ter ae al 600 1000 
25 1250 4/6/9 5 be Siadl pei toy ah 750 1250 


Problems.—Construct a septic tank of the size selected by the instructor. 
Compute materials required; excavate, build forms, and make and place 
the concrete. Concrete plank for the cover may be made above ground, 
and placed when the interior forms of the tanks are removed. 


JOB 95. CONCRETE STEPS 


Practically every home needs one or more flights of concrete 
steps, either leading from the basement or from the front and 
rear entrances, or connecting one walk with another. Concrete 
steps, when well constructed, are firm, durable, safe, and sanitary. 

Forms for steps are usually of wood. For the side forms, 2-in. 


268 CONCRETE PRACTICE 


plank should be used, and 1-in. material is usually satisfactory 
for braces and forms for risers. When desired, the forms for 
risers may be made to cause recessed panels in the risers. Forms 
for steps must be securely staked or otherwise fastened so as 
to be reasonably rigid. The form surfaces which come in contact 
with the concrete should be well oiled or thoroughly wetted a 
short time before the concrete is placed. 

The earth forming the subbase should be thoroughly and uni- 
formly tamped and compacted. Drainage must be provided, 
either by drain tile or a layer of porous material, such as cinders, 
if there is a reasonable chance of water collecting under the steps. 


1x4" Supports 
For Pee ene 


Wall 


Fia. 1382.—Forms and section of concrete steps. 


In general, the concrete mix and consistency used for concrete 
steps should be the same as that used for the construction of 
concrete sidewalks. For separate flights of steps, a 1:2:3 mix 
by volume is recommended. The thickness of the steps at any 
point should not be less than 6 in. Figure 132 shows the method 
of construction of concrete basement steps. Side walls for steps 
in concrete walks may be provided or not, as desired. 

The methods of mixing, placing, finishing, and curing of con- 
crete for concrete sidewalks should be followed when making 
concrete steps. Wood floats should be used for finishing, as 
steel tools may make the surface too slippery. Steel tools are 
necessary for edging and rounding corners, ete. 


ta is 


FIELD WORK 269 


Forms may be removed after a few days. 

The steps should be covered for a day with wet canvas or 
burlap, and then kept wet for a week so that the concrete can 
‘‘cure”’ and “‘harden”’ in the presence of moisture. 


Problems.—Construct a flight of steps as directed by the instructor. 
Compute materials needed, excavate and compact subbase, construct 
forms, mix, place, and finish concrete, cure concrete, and remove forms. 


JOB 96. CONCRETE WINDOW SILLS AND LINTELS 


Precast concrete window sills and lintels have often been used 
instead of cut stone sills and lintels, and with satisfactory results 
in regard to labor required and appearance of the finished work. 
In general, precast sills and lintels are more economical than 
those cast in place in the walls. | 

There are two kinds of sills and lintels, those made in one 
section and those made in two sections. When the sill or lintel 
does not extend clear through the wall, and is not to have room 
plaster applied directly to one side of it, the one-piece lintel: is 
satisfactory. A one-piece sill or lintel must be furred out for 
the lath and plaster, because otherwise water may pass through 
the concrete and show on the plaster. 

The two-piece sill or lintel is one constructed in two sections, 
with an air space provided between the sections. This air 
space is necessary to prevent the passage of water through the 
concrete, or the condensation of water on the inside surfaces. 
The width of the air space may be 14-in. or more, and the space 
must be continuous. Both sections of a lintel should prefer- 
ably be of the same size or about the same size. 

Lintels should be reinforced, so that they can properly carry 
the loads that will be applied to them. At least two reinforcing 
bars should be used for each lintel (one bar for each section, if 
the lintel is in two parts). In general, the cross-sectional area 
of the reinforcement should be from about 34 of 1 per cent to 
1 per cent of the cross-sectional area of the lintel. When placing 
lintels in walls, the reinforced side must be the lower one, that is, 
the reinforcement must be in the bottom of the lintel. 

As the sills do not carry any appreciable load, they do not 
need to be reinforced, except, possibly, to reduce the chance of 


270 CONCRETE PRACTICE 


breaking them in handling. A 14-in. round bar placed about 1 
in. from each corner of the sill will usually be sufficient. 

The table which follows gives the reinforcement needed for 
lintels of various heights and used in different stories of the 
building. This table may be used for designing lintels for 
residences and ordinary store buildings, up to two stories and 
basement in height. For one-story houses, the first-story values 
may be used for the basement lintels, and the second-story 
values for the first-story lintels. For warehouses, larger and 
higher buildings than two story residences, and buildings sub- 
jected to heavy loadings, the design of the lintels should be left 
to the concrete-designing engineer. 


NUMBER AND SIzE OF RounpD Bars REQUIRED FOR REINFORCING LINTELS 
OVER Doors AND WINDOWS 


Basement | | First story | Second story 


Height of lintel in inches 


eee 6 to 9 | 9 to 12 6 to 8 | 9 to 12 6 to 8 | 9 to 12 
opening in 
inches Number and size of bars 
Num- Nu : Num ele Ni : Num . | Num i 
i Size ee Size ees Size ee Size ie Size en Size 
0-28 3 16 2 14 2 16 2 34 2 3¢ 2 36 
28-36 2 54 2 4 2 4 2 3g 2 36 2 | 3% 
36-48 2 34 2 | 54 BA Se 2 16 2) 4 Pa ee a 
48-60 2 4% 2 34 2 34 2 56 2 58 2 44 
60-72 3 as ee Fea oe | 2 1% 29S. 2. | 34 


Notre.—Two bars are to be used for each lintel. Place one bar in each 
section of a two-piece lintel. Bars should be embedded 34 in.. from the 
lower side of the lintel as placed in the wall. 


The forms for concrete sills or lintels may be made either of 
metal or wood. Metal forms are satisfactory when a large 
number of sills or lintels of the same size are to bemade. Wooden 
forms are usually more satisfactory when a variety of sizes and 
only a few sills or lintels of each size are wanted. Glue, plaster, 
or sand molds may be used for making ornamental sills and lin- 
tels, as in making ornamental trim stone. Wooden molds may 
be kept from swelling and warping by giving them one or two 


FIELD WORK 271 


coats of shellac or linseed oil. Just before the concrete is placed, 
the form surfaces should be given a thin coating of form oil, to 
keep the concrete from sticking to the forms. Almost any clear 
oil that will give a thin oil film which will not stain the concrete 
will be satisfactory. 

Forms should be designed so that they can be easily assembled 
and taken apart. The various form pieces should be of the exact 
size and shape required, and should fit together in such a manner 
that they may be easily pulled away from the concrete without 
injuring the surfaces or edges of the sill or lintel. 

When desired, sills and lintels may be made with special sur- 
_ face finishes or facings, according to methods described in See. II. 

The proportions of the mix for concrete for sills and lintels 
should be about 1:2:3 by volume. Fine aggregates should all 
pass the No. 4 sieve, and not over 5 per cent should pass the No. 
100 sieve. Coarse aggregates should all pass the 34-in. sieve, 
and not over 5 per cent should pass the No. 4 sieve. As little 
mixing water should be used as will give a workable mix. Con- 
crete should be thoroughly tamped and worked in the forms to 
give the surfaces desired, free from voids and pockets. 

The amount of hair cracks and crazing may be reduced by 
avoiding an excess of fine material (cement, stone dust, silt), 
by using as little mixing water as necessary, by placing and 
finishing the concrete so that a film of water and fine material will 
not be left on the surface, by not using steel finishing tools, if 
possible, and by keeping the concrete surfaces wet for about 1 
week or 10 days after the concrete is placed. 


Problems.—Estimate the materials required for forms and concrete, 
construct forms, and make some window sills and lintels according to the 
sizes and designs given by the instructor. Note labor required. Com- 
pute complete costs per cubic foot of concrete placed and per sill or lintel 
made. 


JOB 97. PLAIN CONCRETE FLOORS 


In this job, the construction of plain concrete floors laid on the 
ground is considered. Such floors are suitable for basement 
floors, barn floors, small garage floors, etc. 

The following condensed specifications are for plain concrete 
floors, which are to be subjected to light and moderate traffic. 


272 CONCRETE PRACTICE 


They may seem to be a little severe for basement floors for resi- 
dences. ‘These specifications are similar to the American Concrete 
Institute Tentative Standard Specifications for Concrete Floors. 


Condensed Specifications for Plain Concrete Floors Laid on the Ground 
and Suitable for Moderate or Light Traffic 


General Requirements 


Portland Cement.—Shall meet the requirements of the Standard ges 
fications for Portland Cement as given in Appendix 1. 

Fine Aggregate.—Shall consist of natural sand or screenings from hard, 
tough, crushed rock or gravel consisting of quartz grains or other hard 
material clean and free from any surface film or coating, graded from fine 
to coarse with coarse particles predominating. Dry fine aggregate shall 
all pass a No. 4 sieve, not more than 25 per cent shall pass a No. 50 sieve, 
and not more than 5 per cent shall pass a No. 100 sieve. Percentage of 
silt, clay, or loam shall not be more than 5 per cent. Tensile strengthof 1:3 
mortar briquettes should be equal to, or more than, that of standard Ottawa 
sand briquettes of the same mix and consistency. 

Course Aggregate.—Shall consist of clean, hard, tough, uncoated crushed 
rock or gravel containing no soft, flat, and elongated particles, and being 
free from vegetable and organic matter. All coarse aggregate shall be 
well graded, and shall pass a 114-in. sieve, and not more than 5 per cent 
shall pass a No. 4 sieve. 

No. 1 Aggregate for Wearing Courses.—Shall be of equal quality as 
coarse aggregate. All No. 1 aggregate when dry shall pass a 3-in. sieve, 
and not more than 10 per cent shall pass a No. 4 sieve. 

Water.—Shall be clean and fit to drink. 

Reinforcement.—Should in general meet the requirements of the Stand- 
ard Specifications for Steel Reinforcement of the A. 8. T. M. 

Joint Filler.—Should be a suitable compound which will not soften and 
run in hot weather or pone or crack in cold weather, or premolded strips of 
bituminous-filled fiber 1¢-in. thick, and of a width equal to the thickness of 
the floor slab. 

Measuring.—Shall be such as will insure uniform proportions and con- 
sistency at all times. 

Mixing.—Concrete shall be mixed until each particle of fine aggregate 
is coated with cement paste, and each particle of coarse aggregate is coated 
with mortar. A batch mixer is preferred for mixing. 

Retempering.—Retempering or remixing mortar or concrete that has 
partially hardened shall not be permitted. 

Curing.—A freshly finished concrete floor shall be protected from the 
sun, wind, and rain until it can be sprinkled and covered. As soon as the 
finished floor has hardened sufficiently, it shall be covered with an inch of 
wet sand or 2 in. of wet Sawdust, and kept wet by sprinkling with water 
for at least 10 days. 


FIELD WORK 273 


Subgrade.—Shall be well drained and compacted to a firm surface with a 
uniform bearing power. All soft and spongy places shall be removed and 
filled with suitable material well tamped. A drainage system shall be 
provided when necessary. 

Subbase.—When required, only clean coarse gravel or steam-boiler 
cinders free from ash and unburned coal shall be used. Thickness of sub- 
base shall be at least 5 in. Subbase shall be thoroughly compacted and 
wetted before the concrete is deposited. 

Forms.—Shall be free from warp, and of sufficient strength and rigidity. 
Shall be well staked or braced and held to established lines and grades, and 
their upper edges shall conform to the established grades of the floor. 
Forms shall be cleaned and thoroughly wetted or oiled before concrete is 
deposited. 

Size and Thickness of Slabs.—The floor slabs shall be independently 
divided concrete block having an area not more than 100 sq. ft., or dimen- 
sions greater than 10 ft. If larger areas are required, the slabs must be 
specially reinforced. ‘The thickness of the floor slab should not be less 
than 5in. Thickness selected depends upon the loads, subbase, and strength 
of mix. 

Joints.—When required, }4-in. joints shall be left between the slab and 
walls and columns of the building. 

Edges.—Unless protected by metal, edges of slabs should be rounded 
to a radius of 4 in. 

Consistency.—The least amount of mixing water that will give a work- 
able mix shall be used for concrete and mortar mixes. 

Reinforcement.—Slabs having an area of more than 100 sq. ft. or dimen- 
sions greater than 10 ft. shall be reinforced with wire fabric, or with plain 
and deformed bars. The reinforcement shall weigh not less than 28 lb. 
per 100 sq. ft. of floor surface. The reinforcement shall be placed upon, 
and slightly pressed into, the concrete base immediately after the base is 
placed. It shall not cross joints, and shall be lapped sufficiently to develop 
the full strength of the metal. 


Two-course Plain Concrete Floors 


Proportions for Base Course.—The concrete shall be mixed in the pro- 
portions by volume of one sack of portland cement, 24 cu. ft. of fine aggre- 
gate, and 5 cu. ft. of coarse aggregate. 

Placing Base Course.—After mixing, the concrete shall be handled 
rapidly and the successive batches deposited in a continuous operation, 
completing individual sections of the required depth and width. Under 
no circumstances shall concrete that has partly hardened be used. The 
forms shall be filled, and the concrete struck off and tamped to a surface, 
the thickness of the wearing course below the established elevation of the 
floor. The method of placing the various sections shall be such as to pro- 
duce a straight, clean-cut joint between them, so as to make each section an 
independent unit. If dirt, sand or dust collects on the base it shall be 
removed before the wearing course is applied. Workmen shall not be 


274 CONCRETE PRACTICE 


permitted to walk on the freshly laid concrete. Any concrete in excess of 
that needed to complete a section at the stopping of work shall not be used. 
In no ease shall concrete be deposited upon a frozen subgrade or subbase. 

Proportions for Mixture No. 1 for Wearing Course.—The wearing course 
shall be mixed in the proportions of one sack of portland cement and 2 cu. ft. 
of fine aggregate. The minimum thickness shall be 34 in. 

Proportions for Mixture No. 2 for Wearing Course.—The wearing course 
shall be mixed in the proportions of one sack of portland cement and one 
cubic foot of fine aggregate and one cubic foot of No. 1 aggregate. The 
minimum thickness shall be 34 in. 

Mortar Consistency for Wearing Course.—The mortar shall be of the 
driest consistency possible to work with a sawing motion of the strikeboard. 

Placing Wearing Course.—The wearing course shall be placed immedi- 
ately after mixing. It shall be deposited on the fresh concrete of the base 
before the latter has appreciably hardened, and brought to the established 
grade with a strikeboard. In no case shall more than forty-five minutes 
elapse between the time the concrete for the base is mixed and the wearing 
course is placed. 

Finishing Wearing Course.—After the wearing course has been brought to 
the established grade by means of a strikeboard, it shall be worked with a 
wood float in a manner which will thoroughly compact it and provide a 
surface free from depressions or irregularities of any kind. When required, 
the surface shall be steel-troweled, but excessive working shall be avoided. 
A mixture of dry cement, sand and No. 1 aggregate may be applied to the 
fresh concrete of the base for a wearing course, but in no case shall dry 
cement or a mixture of dry cement and sand be sprinkled on the surface of 
the wearing course to absorb moisture or to hasten the hardening. Special 
methods not conflicting with these specifications may be used. 

Coloring.—If artificial coloring is employed, only mineral coloring matter 
shall be used, and it must be incorporated with the entire wearing course, 
and shall be mixed dry with the cement and aggregate until the mixture is 
of a uniform color. In no case shall the amount of coloring exceed 5 per 
cent of the weight of the cement. 


One-course Plain Concrete Floors 


Proportions.—The concrete shall be mixed in the proportions of one 
sack of portland cement to not more than 2 cu. ft. of fine aggregate and not 
more than 3 cu. ft. of coarse aggregate, and in no case shall the volume of 
the fine aggregate be less than one-half the volume of the coarse aggregate. 

A cubic yard of concrete in place shall contain not less than 6.8 cu. ft. 
of cement. 

Placing.—(This is the same as for placing base course of two-course 
floors. ) 

Finishing.—After the concrete has been brought to the established grade 
by means of a strike board, and has hardened somewhat, but is still work- 
able, it shall be floated with a wood float in a manner which will thoroughly 
compact it and provide an.even surface. When required, the surface shall 


FIELD WORK 275 


be steel troweled, but excessive working shall be avoided. Unless pro- 
tected by metal, the surface edges of all slabs shall be rounded 14 in. 


When desired, a terrazzo floor finish may be applied to any 
concrete floor. 

A concrete floor surface may be made satisfactory for dancing 
by applying liquid soap and rubbing this soap into the pores of 
the concrete with a scrubbing brush. An application of pow- 
dered soap to a treated floor helps to keep-it in condition. 
Another method is to apply paraffin wax, dissolved in turpentine, 
in sufficient quantity to fill the pores of the concrete. After 
the turpentine has evaporated and the floor surface is dry, 
powdered wax should be applied as in the case of a wooden floor. 

There are various methods of treating concrete surfaces, which 
have been previously described in the text. When desired, most 
any of these methods may be used for treating concrete floor 
surfaces. 


Problems.—a. Observe the construction of a concrete floor, noting 
preparation of subgrade and subbase, forms, dimensions and thickness of 
concrete slab, one- or two-course floor, proportions of mix, consistency, 
concrete plant, reinforcement, mixing, placing, finishing, curing, etc. Note 
organization of crew and labor hours required for each part of the work. 

b. Construct a one-course concrete floor as directed by the instructor: 
(1) preparing a complete estimate of all materials, plant, and labor needed; 
(2) preparing the subgrade, subbase, and forms; (3) mixing, placing, and 
finishing the concrete; and (4) curing the concrete. Keep records of all 
materials and labor used. 


JOB 98. CONCRETE CULVERTS—SPECIFICATIONS AND 
ESTIMATES 


Concrete culverts are of three kinds: pipe, box, and arch. 
Pipe culverts are usually the most economical for small areas, 
while box and arch culverts are needed for larger areas. The 
selection of a culvert depends upon the size and character of 
the drainage area, available head room, depth of fill, kind of 
foundation, and the opinion of the person selecting the culvert. 
Sometimes box and arch culverts are built without a floor, and 
are called open-box or open-arch culverts. The present practice 
is to provide concrete floors for all concrete culverts unless the 
natural bed or floor should happen to be of comparatively hard 


276 CONCRETE PRACTICE 


bedrock, so that the side walls will not be undermined by water. 

A culvert, in order to be efficient, should have the same general 
direction as the flow of the stream; the bottom of the culvert 
should be lower at the discharge end than at the head end; the 
slope or inclination of the culvert bed should be about the same 
as that of the stream; the head walls or wings should be arranged 
to help the flow of the water; and there should be no projections 
in the culvert bed or obstructions near the entrance or discharge 
ends which would interfere with, and reduce, the free flow of the 
water. In general, the culverts should be placed across road- 
ways and in the direction of the stream flow. 

The size of the waterway or the culvert cross-sectional area 
required depends upon the maximum rate of rainfall, area and 
shape of the watershed, kind and condition of the soil, and the 
character and slope of the drainage surface and stream bed. 
The best way of determining the culvert area needed is to 
observe the flow of the stream during flood times, and to measure 
the cross-section of the stream at some narrow place near the 
culvert site. 

When stream data is not available or reliable Talbot’s formula 
may be used for finding the required culvert area. This formula 
Lee 


A = Cw/D3 
where A = area of waterway in square feet 
D = drainage area in acres 


C =a coefficient, depending on the character of the 
drainage area 


C varies from 24 to 1 for steep and rocky ground; it equals 
about 14 for rolling agricultural country subject to floods due to 
melting of snow, and with a valley length of three to four times its 
width; and equals about 1, or less, in localities not affected by 
floods due to melting snow, or where the valley length is many 
times the width. 

C should be increased for steep side slopes, especially when the 
upper part of the valley is much steeper than the channel near 
the culvert. 

The following table gives the area of waterway required for 
various drainage areas: 


a 


FIELD WORK Bit 
WATERWAY OR CULVERT AREA REQUIRED 


eteste area in Steep slopes Rolling country Flat country 


aaa Culvert area in square feet 
10 5.6 1.9 1.1 
20 9.4 3.1 1.9 
30 12.8 4.3 2.6 
40 16.0 5.3 one 
50 19.0 6.3 3.8 
60 21-5 fas 4.3 
80 at 9.0 5.4 
100 a2 1025 6.3 
125 ol 12,5 fee 
150 43 14.5 8.6 
200 aps 18 10.5 
300 fie. 24 15 
400 89 30 18 
600 121 40 24 
800 150 50 30 
1000 178 59 36 


The length of the culvert. will depend upon the width of the 
roadway and the depth of fill on top of the culvert. The slope 
of the earth fill can usually be taken as one and one-half horizon- 
tal to one vertical. In highway construction, the width of road- 
way should not be decreased at a culvert, as such practice is 
dangerous. 

Head walls and wings should be built so that the embankment 
is protected and the flow of the water aided. These wings may 
be placed parallel with, or at right angles to, or inclined (usually 
30 to 45 deg.) with, the axis of the culvert. Wings parallel to the 
roadway are often used for small culverts with low fills, and the 
wing walls are built up above the grade line to provide a guard 
rail. Flared wings are better on deeper fills, as these wings 
facilitate the flow of water and are economical in the amount of 
concrete required. Wings parallel to the axis of the culvert are 
sometimes used when the culvert is likely to be made longer in 
the near future. In general, the head walls and wings should be 
long enough to keep the culvert opening clear when earth falls 
around the ends. 


CONCRETE PRACTICE 


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FIELD WORK 279 


Pipe culverts of cast iron, corrugated iron, vitrified clay, and 
plain and reinforced concrete are suitable in many places. Cor- 
rugated iron for small pipe culverts and reinforced concrete pipe 
for the larger sizes seem to be preferred at present. All pipe 
culverts should have concrete head walls to protect the embank- 
ments and the ends of the culverts. Reinforced concrete pipes 
up to about 6 ft. in diameter have been used. 

Concrete box and arch culverts of many types have been 
designed and used. Most every State Highway Commission and 
Railroad Company has its own set of standards for these kinds of 
culverts. The design of a box or arch culvert depends upon the 
foundation conditions, depth and character of the soil, and 
loadings to be applied. Culverts of more than 6-ft. span are 
frequently classified as bridges. 

Figure 133 shows a standard design of a concrete box culvert 
with sloping end walls prepared by the engineers of the Wisconsin 
Highway Commission. 

Specifications for concrete materials and for concrete for plain 
and reinforced concrete culverts vary in different localities. The 
specifications of the Wisconsin Highway Commission for Concrete 
in forms given in Job 36, are typical. Clauses not applying to 
the particular job are omitted or crossed out. Class A concrete is 
preferred for the standard concrete box culverts. 

Forms for culverts are often constructed of 2-in. plank, well 
supported, braced, and tied in place. Forms for the interior of 
a box culvert should be so made that they can be readily removed 
without damage to the concrete. Wedged braces may be used, 
with the wedges so made and placed that they can be readily 

removed. 

The concrete should be allowed to cure or harden for at least 
3 weeks in hot weather, or longer in cold weather, before the 
forms are removed. Exposed concrete surfaces should be pro- 
tected from the rays of the sun and dry winds during the curing 
period. When practicable, the exposed surfaces should be 
covered with damp sand and kept wet for 1 week or 10 days after 
the concrete has attained initial set. If a surface covering is not 
practicable, then the concrete should be sprinkled twice a day. 


Problems.—Prepare the materials estimate for the Wisconsin Highway 
Commission Concrete Box Culvert shown in Fig. 133, assuming an 18-ft. 


280 CONCRETE PRACTICE 


roadway and a fill of 6 ft. over the top of the culvert. Estimate excavation, 
forms, reinforcement, cement, sand, and crushed rock, assuming Class A 
concrete. If an actual culvert is to be constructed, the roadway width, fill, 
culvert length, etc., in this job should be changed to conform with those 
for the culvert to be built. 

Prepare an estimate of the labor required for this culvert, subdividing 
the estimate as follows: excavation, forms, bending and placing reinforce- 
ment, mixing and placing concrete, removal of forms, and backfilling. 


JOB 99. CONCRETE BOX CULVERTS—EXCAVATION AND STAKING 
OUT 


The best way is to stake out and construct the culvert before 
the fill is placed. When the fill is already in place, the dirt must 
be excavated to the bottom of the culvert floor. The bottom of 
the excavation should be true to grade and alignment. All soft 
and spongy places in the soil should be removed and replaced 
with good earth, well tamped to give a uniform bearing power. 
It is important that the dirt forming the subgrade be firm and 
compact to give a uniform bearing power. ‘Trenches for the cut- 
off walls at each end of the culvert must be dug. The slope of 
the excavation should be such that there will be no trouble due 
to dirt sliding down on the subbase, or into the forms. 

In staking out a culvert, stakes are driven to give the elevation, 
slope, or grade and alignment of the top of the culvert floor, as 
well as the general overall dimensions of the culvert. In general, 
the culvert will extend crosswise of the roadway, and its align- 
ment and slope will conform to that of the waterway. Care 
should be taken not to have the culvert floor too far above or 
below the bed of the waterway, or too far out of alignment so as 
to obstruct the flow of water, or to reverse the slope of the culvert 
floor. This slope should preferably not be less than 14 in. to the 
foot. A convenient bench mark and reference stakes (offset a 
given distance to the side of the center line of the culvert) should 
be provided for the purpose of checking the elevation and slope of 
the culvert floor. 


Problems.—a. Observe the staking out of a culvert, noting just what 
stakes are set, how they are set, and where. 

b. Stake out a culvert. This culvert may be assumed to be placed under 
an existing roadway, or to be for a proposed new roadway. An engineer’s 
level, level rod, and measuring tape should be used if available. Satisfactory 
work may be donewith a good carpenter’s level, straightedge, and measuring 


| 
: 
; 


FIELD WORK 281 


tape, if engineering instruments are not to be had. Draw a sketch showing 
location of the roadway and all stakes set. If any excavating is needed, this 
should be done, noting quantity of dirt removed and labor hours required. 


JOB 100. CONCRETE BOX CULVERTS—FORMS AND REINFORCE- 
MENT 


The forms used for large concrete culverts are usually of 2-in. 
plank well braced and tied. For smaller culverts, 1-in. boards 


SW 


Fia. 135.—Forms for 10 X 10 ft. reinforced concrete box culvert, C. B. & Q. Ry. 


may be used, if they are supported and held in place by cross- 
braces placed fairly close together. Figures 134 and 135 should 
be examined for details of culvert forms. 


282 CONCRETE PRACTICE 


Care should be taken in the design of the forms so that they 
will be firm and unyielding, and yet be economical in regard to 
lumber and be easy to remove. Wedges, with the braces of the 
inside forms of a box culvert, aid in making these forms easy to 
remove. 

The reinforcement bars should be carefully placed in position 
and wired together, so that they will not be displaced during 
concreting. 

Problems.—a. Observe the construction of forms for a concrete box 
culvert, noting size and dimensions of the culvert, amount, kind, and dimen- 
sions of form lumber used for different parts of the forms, ties, braces, 
wedges, etc. Make sketches of the forms, if these sketches will help illus- 
trate and explain the form construction. Note labor hours required, and 
number of square feet of form surface. Observe how the reinforcing rods 
are placed and secured in position. 

b. Make a bill of material for the form lumber. Make sketches for the 
design of the form, if such sketches are needed. Construct the form for the 
culvert staked out in the preceding jobs, noting labor hours required. 
Place reinforcement bars in forms and secure them in position, noting labor 
hours required. 


JOB 101. CONCRETE BOX CULVERTS—CONCRETING 


Before starting concreting, the materials should be on the 
job, and the plant clean and in working order. Sometimes the 
mixer can be placed high enough above the culvert forms so that 
the concrete can be chuted into the forms. - Usually runways and 
barrows or carts are used for transporting concrete. 

The concrete is poured monolithic up to the construction joint, 
then the inside forms and the reinforcement bars for the top of 
the culvert are placed in position and the concreting finished. 
These inside forms should be previously prepared, so that they 
can be placed without appreciably interrupting the process of 
concreting. With good planning, the delay in concreting 
should not be over 20 or 30 min. 

If more than 45 min. are required for the placing of the inside 
forms, the concrete surface at the construction joint should be 
roughened, cleaned of all loose concrete material, debris, and 
laitance, and a coat of cement grout applied before any new 
concrete is placed. 

As the concrete is placed in the forms, it should be spaded so 
as to push the large aggregate away from the form surfaces and 


LF >. ee 


FIELD WORK 283 


to remove air pockets. A little tamping may be advisable 
thoroughly to compact the concrete in place. 

All exposed edges should be rounded, and the exposed surfaces 
of the concrete should be finished when the concrete is placed. 


Problems.—a. Observe the concreting of a concrete box culvert, noting 
the plant layout, organization of crew, method of placing concrete, amount 
of concrete placed, and time required. 

b. Arrange the plant, organize crew, and mix and place concrete in the 
concrete box culvert forms constructed in the previous job. Note amount of 
concrete placed and labor hours required. 


JOB 102. CONCRETE BOX CULVERTS—REMOVING FORMS 


After the concrete has hardened, the forms should be removed 
in such a manner that the concrete will not be damaged. Con- 
crete should be from 14 to 28 days old in warm weather, and older 
in cold weather, before the forms are removed. 

After the forms are removed, the concrete surfaces should be 
gone over, fins and projections removed, and holes and spongy 
places dug out and patched. 

The form lumber removed should be separated, nails removed, 
surfaces cleaned, and then piled for removal to another job. 

The backfilling should now be done. The dirt should be 
placed in layers about 6 in. thick, and each layer tamped and 
compacted before the succeeding layer is placed. If a supply of 
water is available, thoroughly wetting the backfill will help 
settle the dirt. 


Problems.—a. Observe the removal of forms, concrete surface cleaning 
and repairing, and backfill on a concrete box culvert Job, noting amount of 
work done and labor hours required. 

b. When the concrete of the box culvert made in previous jobs is 3 weeks 
old, remove the forms, and separate, clean, and pile the lumber; clean and 
patch concrete surfaces; and make all needed backfill, noting amount of work 
of each kind and labor hours required. 


~JOB103. CONSTRUCTION OF REINFORCED CONCRETE BUILDINGS 


The successful and economical construction of a reinforced 
concrete building requires very careful planning in regard to 
plant, forms, labor, rate of progress, and other construction 
details. As a building is larger and more complicated in detail 
than most of the structures described in previous jobs, the profit- 


284 CONCRETE PRACTICE 


able construction of the building will, consequently, require 
much more care and thought. 

The estimates for plant, materials, labor, and costs should 
be carefully made according to the principles given in Sec. IV. 

The correct planning of the work is important. The prepara- 
tion and use of progress charts, work schedules, and material 
schedules are almost a necessity on large jobs, and are an aid on 
smaller and medium-sized jobs. 

The choice of plant, plant layout, materials storage, and simi- 
lar items must be carefully thought out in advance. Sketches 
for the plant layout should be prepared 
on all large jobs. 

The excavation for the basement will 
usually be made according to the methods 
already given, except that trucks with 
a steam or gas shovel or drag line will 
probably be used on largejobs. Inmany 
instances, the walls of the excavation 
will need to be braced. A pump may be 
required for the removal of ground water. 
In special cases, it may be necessary to 
, shore up or underpin the walls of adja- 
Fic. 136.—Isolated footing. cant buildings. 

After the excavation is completed, the building foundations 
are constructed. ‘These foundations may be in the form of 
separate or isolated footings for each of the columns and walls; 
combined footings (including the so-called cantilever footings), 
when one or more columns are carried by one footing; continu- 
ous footings, when the footing is continuous under a row of 
columns; and raft footings, which extend over the whole lot, 
support all columns, and are built monolithic. Raft footings are 
frequently used when the soil has but comparatively low support- 
ing power. Piles are used under the footings when so required 
by soil conditions. Concrete footings (either plain or reinforced) 
appear to be the most economical at the present time. 

The formwork; steel bending and placing, and pouring of 
concrete for the foundations rarely cause any trouble. 

Location or key plans showing the location of columns and 
beams are almost necessary on all reinforced concrete building 


Neen s/eps 
outsive This 


Outline for 


gsteped | Ashped 
footing | footing 


FIELD WORK 285 


SB EREOM ¥ 
Fig. 137.—Combined footing. 


Wa 
S NAL (GAY _Ik 
ir MH REY 
bF"2; gf? ‘ 


Neer 


Note.- Heavy dot and dash lines indicate stee/ in fop dak 
Heavy dotted lines indicate steel ip bottom 


Fic. 138.—Raft foundation. 


286 CONCRETE PRACTICE 


jobs. <A general assembly plan of the formwork is a great help 
to the carpenters. Details of all general and special formwork 
should be drawn, and blueprints secured for the use of foreman 
and carpenters. 

Utah Street 


Lincoln Avenue 
Grant Flace 


Montana Street 


Fia. 139.—Location or key plan. 


Most of the details of the construction of the forms for the 
columns and floors have already been covered in the preceding 
parts of the text. Metal column forms are frequently used. 


Girder Foun 


) 
zh 
7 sy 


ms 


“~-.Celumn Forap 


@ 
a 
NY, 
oe 


Fig. 140.—General assembly plan. 


Both matched and edged lumber are commonly used for floor 
forms, though metal floor forms are gaining in favor. 

The accurate bending, placing, and secure fastening or anchor- 
ing of the reinforcing steel in position are essential. Blueprints 
showing beam and reinforcing bar details are necessary. 


FIELD WORK 287 


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fqce of wa// § 


uth & 
inet floor 
| | a SS ER | ER GE Rete 
: H S 
; j I; Sixth floor i 
S 
i Aa) 
> i Fifth |_| floor 


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FLAT SLAB CONSTRUCTION BEAM AND GIRDER CONSTRUCTION 
Fig. 142.—Cross sections of reinforced concrete buildings. 


288 CONCRETE PRACTICE 


The concrete mixes used are invariably given in the plans and 
specifications. Mixes are usually proportioned to give a 28-day 
unit compressive strength of 2000 lb. per sq. in. or greater. 

Columns are usually poured up to the bottom of the column 
capital and allowed to set 24 hr. before pouring the capital and 
floor slab. Whenever practicable, the column capitals and floor 
slabs and beams for any one floor should be poured in a single 
operation. 

Forms should not be removed too soon, especially in cold 
weather. In general, the beam and floor-slab forms should be 
designed and built so that they may be removed without dis- 
turbing some of the props or shores which support the beams and 
slabs. Props should not be removed until it is certain that the 
concrete has hardened and attained enough strength easily to 
carry the loads placed upon it. 

After the forms are removed, all fins and other projections 
should be removed, porous places cut out and patched when 
necessary, and the exposed concrete surfaces finished as required 
in the plans and specifications. 

In most commercial and factory buildings, a cement floor 
finish is usually applied integral with the floor slab. In some 
instances, the cement floor finish is applied after the floor slab 
has hardened. Some other types of finish commonly used are 
terrazzo, tile, asphalt, linoleum, brick, steel plates (for trucking 
aisles), wood block set in asphalt, and various types of wood floors. 
Tile floors are commonly used in entrances, corridors, lobbies, 
vestibules, and toilets. Asphalt floors are suitable where water- 
proof floors are desired. Brick and wood block floors are suit- 
able where heavy trucking occurs. Finished wood floors of oak, 
maple, or birch are often desired. Sleepers (about 2 X 3 in. in 
size and placed 16-in. on centers) are set on, and anchored to the 
floor slab. A layer of waterproof building paper is placed on top 
of the sleepers, and then the finished flooring is laid. Sometimes 
the space between the sleepers is filled with lean cinder concrete. 
Floor coverings, such as linoleum, are suitable for offices, corri- — 
dors, schoolrooms, ete. 

Various types of roofings have been used for reinforced concrete 
buildings. A cement-finish roof surface is satisfactory when 
absolute dryness is not required. Cement roof finishes tend to 


FIELD WORK 289 


erack in time, and thus cause small leaks. An asphalt coating, 
using asphalt with a high melting point, gives fairly satisfactory 
service, but must be renewed every year or so. The same is true 
of special roof paints. <A built-up pitch and gravel roof, like the 
Barrett Specification Roof, is widely used on reinforced concrete 
buildings and gives satisfactory service. A built-up asphalt 
roofing (layers of asphalt and rag or asbestos felt) gives 
satisfactory service, when properly constructed. Clay tile 
roofings are used in cases where certain architectural effects are 
desired. 

Walls in reinforced concrete buildings may be of concrete, 
brick, or clay tile covered with cement plaster. Concrete walls 
are usually preferred for the basement, and brick for the exterior 
walls of the other stories. 

Partitions in the building may be constructed of reinforced 
concrete, brick, clay tile, gypsum tile, metal lath and plaster, 
wood lath and plaster, plaster board, wood, or various combina- 
tions of the materials mentioned as desired. 

Other work in a reinforced concrete building, such as heating, 
plumbing, electric wiring, glass and glazing, roofing and flashing, 
painting, etc., is usually let as separate or subcontracts. This 
work must be considered when preparing estimates for the com- 
plete building. It is customary to secure separate bids for each 
of the items mentioned. 


Problems.—a. Observe the construction of a reinforced concrete building 
noting all things of interest. If time permits, separate studies may be 
made of the excavation, concreting plant, forms and forming, bending and 
placing reinforcing steel, concreting, removal of forms, and surface finishing. 

b. Secure a copy of the plans and specifications of a small reinforced 
concrete building, and prepare a complete estimate of the plant, materials, 
labor, and cost. 

c. In addition to the preceding problem, design the plant layout and 
prepare work schedules and progress charts for constructing the building. 


Lee 104. CONSTRUCTION OF REINFORCED CONCRETE SLAB AND 
GIRDER BRIDGES 


Simple reinforced concrete slab and girder bridges and their 
abutments may be built in one of the following ways: (1) the 
abutments and bridge may be cast as a monolithic structure; (2) 
the abutments may be constructed first and the bridge cast in 


290 CONCRETE PRACTICE 


place on the abutments; or (3) the abutments may be built on 
the job and bridge cast in a convenient place, and later hauled to 
the job and placed on the abutments. ‘The first method has been 
used for bridges of short spans; the second method for bridges of 
all spans; and the third method in instances where it is not 
desirable to interrupt or detour traffic for more than a short time, 
as in the construction of a railroad slab or girder bridge over a 
highway. 

The estimates of materials, labor, and costs may be prepared 
according to the principles of Sec. IV. 

The staking out of the bridge and its abutments should be 
done by a competent engineer. 

The excavation for the abutments should then be made, using 
a cofferdam and pumps, if necessary. If required, piles should 
be driven to support the abutments. Then the forms for the 
abutments are erected, the reinforcing steel placed and secured, 
and the concrete poured. Care should be taken to insure that 
the proportioning, mixing, and placing of the concrete conform 
to the specification requirements. After the concrete in the abut- 
ments has hardened sufficiently, the forms may be removed, and 
the surface of the concrete cleaned, fins and projections removed, 
porous places cut out and patched, and exposed surfaces finished 
as required. 

The forms for the bridge proper are now constructed, the steel 
placed and secured in position and the concrete poured. ‘The size 
of the average bridge is nearly always such that the entire bridge 
may be poured in one operation. It is usually advisable to start 
pouring at both ends and finish in the middle of the span, 
though some prefer to start pouring in the center and finish at the 
ends. After the concrete has hardened (not less than about 28 
days even in warm weather) the forms may be removed and the 
surface cleaned and finished as required. 

When the abutments and bridge are cast as a monolithic 
structure, the forms for the entire structure are built at one time. 
Concrete is poured in both abutments simultaneously. When 
the abutment forms are filled, the concrete is placed in the bridge 
forms, beginning at the abutments and ending in the center of 
the bridge. If all of the concreting cannot be completed at one 
operation, the time interval should occur between the pouring 


FIELD WORK 291 


Triangular Moulding ° 


é‘Facing 


2° B°XS '- 3906 
ex" 


eke 7g, 9%8'06'9 
EA, 


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TT EE Hh 
SUT ES CE SE AE 
8X8'x 1619. 2°x4’ Wedges ci aia ghee 7, 
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ue 8'7" & 
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si 5 
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Lar So 


Detail of Wedges 


10"? Pile 8'19 


Longitudinal Section. Cross Section 


Fia. 143.—Formwork for through concrete bridge of 60 ft. span and 16 ft. road- 
way. 


Fig. 144.—Formwork for multiple-span through girder bridge. 


292 CONCRETE PRACTICE 


of the abutments and the pouring of the bridge. When pouring 
is resumed after a time interval, care must be taken to secure a 
good bond between the old and the new concrete. . 

Illustrations of forms for small slab and girder bridges are 
shown in Figs. 143, 144, and 145. 

Some camber should be provided to improve the appearance 
of slab and girder bridges. About 1% inch per ft. of span length 
is sufficient. This would mean 1 in. for a 40-ft. span. 

The proportions of the concrete mix for the abutments and 
the bridge are invariably given in the plans and specifications. 


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Fia. 145.—Forms and falsework for a deck girder highway bridge. 


In general, leaner mixes than a 1:2!4:5 for abutments, and a 
1:2:4 for bridges, or mixes giving a 28-day unit compressive 
strength less than about 2000 lb. per sq. in. should not be used. 

The concreting plant used will depend upon the amount of 
concrete to be poured and upon what the contractor has available 
for the work. The size of the mixer may vary from a two-bag 
to a six-bag mixer. One contractor may use runways and carts 
or barrows, while another may have towers chutes, and spouts. 


Problems.—Inspect the construction of a slab or girder bridge and note 
details regarding the size of bridge and abutments, the construction of the 


FIELD WORK 293 


form work, the placing of the reinforcing steel, the concreting plant, the 
proportions of the concrete mixes used, the time required for pouring, 
the removal of forms, the surface finishing, and any other information of 
importance. Use sketches when these will aid in describing the work. 


JOB 105. CONSTRUCTION OF REINFORCED CONCRETE ARCH 
BRIDGES 


The construction of a reinforced concrete arch bridge is divided 
into several parts such as: the construction of the piers and 
abutments; the erection of the centering and arch formwork; 
the placing of the steel reinforcement; the pouring of the con- 
crete, the removal of the forms and coe ; and the finishing 
of the concrete surfaces. 

The staking out of the arch bridge should be done by a com- 
petent engineer. 

The estimates of materials, labor, and costs may be prepared 
according to the principles given in Sec. IV. 

The details of construction of the piers or abutments will 
vary greatly on different jobs. In some instances, the excava- 
tion, formwork, and concreting can all be completed without 
interference from water. In other instances, cofferdams and 
pumps may be needed to keep out the water while the bridge 
foundations are built. Piling is usually required under the piers 
and abutments, unless good rock can be found at a suitable 
depth. At the present time, most of the bridge foundations are 
built of reinforced concrete resting on solid rock or piles. 

The centering for a concrete arch is the falsework used to 
support the forms for the concrete of the arch. This falsework 
is usually constructed of wood, though steel centering frames are 
sometimes used. Steel centering may not be economical, unless 
there are several spans of equal dimensions so that the centering 
can be used several times. 

Trestle centering is commonly used for small arches. The 
arch forms are supported on transverse caps, which, in turn, are 
supported by posts or piles sway braced and line girted, as in 
an ordinary trestle. Figures 147 and 148 illustrate this type of 
centering. Note the location and size of wedges used for remov- 
ing the centering, after the concrete has hardened. 

In truss centering, a truss forms, or is used to support, the false- 
work for the arch. The truss is supported at each end. The 


CONCRETE PRACTICE 


294 


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FIELD WORK 295 


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Tea ere 
Senn 


Springing Line 
Eley, 225.90“ 


. an Mud Sills if required 6 Eley. E19,00 
4 ANI sills To be laid on 


solid surface blocked 
Elevation where necessary 


All lumber fo be Yellow Pine uriless 


otherwise stated- All bolts, 2” °witt ee 

two standard C./. washers + Lagging fo be me 

matched and dressed to a uniform thickness’ ag hehe eee 

50 as fo form @ smooth and true surface. 

G!! lagging to be 2"x4" tongue and groore ae 2 ) 
— a 40 . c- 
t - 2x 4 Lagging ; i 


ie 
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1 a a a, 


a’ 3" IM TW TW i 
tlhe 0) a2 Sie S ee Se a ae 
SOG PE A ER SS NSN ARS SRY” A EEN Ex4x2-0 
White Oat White Oak. 
Wedges 
& 
Q 
& 
bo) 


ee rr re, 


ee ee ee 


Section A-A 
Fig. 147.—Details of arch centers for Center Strect bridge, Phillipsburg, N. J. 


296 CONCRETE PRACTICE 


forms for the arch are supported by short bents, which rest on 
the upper panel points of the truss. 


oe 


Fia. 148.—Centering for Oswego Arch, Clackamas County, Oregon. Trestle 
type of rib centering. 


When it is not permitted to have trestles or trusses underneath 
the arch forms, these forms may be supported by suspension 
cables, as shown in Fig. 149. The main cables run over towers 
and are anchored on shore. 


Fic. 149.—Suspended centering. 


In erecting arch centers, allowance should be made for camber 
and for shrinkage and settlement of the centering. ‘The camber 
is usually computed and added to the grade elevations on the 
plans, so that the plan elevations give the needed camber. In 


FIELD WORK 297 


addition to the camber, the elevations shown on the plans should 
be increased to care for shrinkage and settlement of the center- 
ing under the load. The amount to provide for this will depend 
on such things as the load, type of centering, size of members, and 
the method of support. 

The lagging for panel arches is generally placed on longitudinal 
beams or joists supported at the falsework panel points. These 


n\eu 


penn nan - 99 fe 
ee 


Fig. 150.—Curved lagging beams for barrel arch centering. 


curved beams are cut to the true curve of the arch intrados 
(underside of the arch), and may be laid off either from the arch 
radii in a loft or yard, or as shown in Fig. 150. 

After the centering and forms for the arch are erected, the 
reinforcing steel should be bent, placed, and secured in position 
as directed in the plans and specifications. 


Fig. 151.—Sequence of pouring arch ring. 


The concreting plant used will vary from a 2- or 3-bag mixer, 
with runways and carts, to a 5- or 6-bag mixer with tower, chutes, 
spouts, etc., depending on the size of the job and the contrac- 
tor’s equipment available. 

Small concrete arches (with spans less than 80 ft.) are usually 
poured in one operation. The pouring must be done in such a 


298 CONCRETE PRACTICE 


manner as to load the centering evenly and symmetrically. The 
simplest way is to start at both springing lines simultaneously, 
and to finish at the crown. 

When the arch is of such size that the pouring cannot be com- 
pleted in one operation, because of the shrinkage stresses and of 
the length of time required, such spans may be poured in longi- 
tudinal sections or by the ‘“‘voussoir’”’ method. The voussoir 
method is better than the longitudinal section method. 

In the voussoir method, the arching is divided into sections 
about as shown in Fig. 151, and these are poured in sequence 
according to the numbering of the sections. With this method 
of pouring, the concrete in the arch rib cannot take any load as 
an arch until after the last section has been placed. Hence, any 
slight settlement or shrinkage of the centering will not cause the 
green concrete to be loaded. 

The centering for concrete arches should not be removed until 
the concrete has hardened enough to carry the loads. A time of 
about 4 weeks is required in warm weather, and a longer time is 
desirable and often necessary in cold weather. ‘The centering 
should be released very gradually. The crown should be released 
first, and then the two flanks simultaneously. It is a good plan 
at first to just start all of the wedges, and then to remove the 
wedges in order as directed. In a series of arches, all centers 
between abutments or piers should be lowered simultaneously. 

After the removal of the forms, all fins and projections should 
be removed and all porous places cut out and repaired. Surface 
finishing, of the kind required in the plans and specifications, 
may now be done. 

Problems.—Inspect the construction of a concrete arch, noting details in 
regard to the construction of piers and abutments, arch centering and forms, 
placing of reinforcing steel, pouring of concrete, removal of centering, and 
surface finishing. Note the general dimensions of the arch and any other 


data of importance. Use sketches as an aid in describing any of the con- 
struction work. 


JOB 106. MANUFACTURE OF CONCRETE BLOCK OR BRICK 


The essential parts of a modern concrete products plant are 
about as follows: 

A storage space for cement, fine and coarse aggregates. 
Cement must be stored in a weatherproof building, and it is advis- 


FIELD WORK 299 


able to store aggregates where they will be partially or wholly 
protected from the weather, especially in winter time. 

A building for housing the machinery and making or manu- 
facturing the concrete masonry units. This building houses the 
mixers and casting machines and molds. 

A building for the accelerated curing of the concrete products, 
if such methods are used. 

A storage space for the concrete products, where they can 
complete their curing or aging before being shipped. 

Of course, a plentiful supply of good aggregates and water, as 
well as shipping facilities, are also essential. 

Large plants give much study to the quality of the aggregates, 
the proportions and consistency of the mix, the methods of 
weighing and measuring the materials, the methods of mixing 
and molding, methods of curing, labor-saving machinery, all- 
year work, economical layout of the plant, as well as other 
questions involving the procuring of the raw materials, the manu- 
facture of the concrete products, and the marketing of manu- 
factured articles. 

Refer to Job 31 and Appendix 11 for further information in 
regard to concrete block and brick. 


Problems.—a. Visit a concrete products manufacturing plant and observe 
the following: plant layout (a sketch of this will help), methods of receiving 
- and storing materials, kinds of products, proportions of mixes, consistency, 
kinds of machines used for mixing and molding, weighing and measuring 
devices, labor-saving machinery in general, methods of curing, storage of 
manufactured products, and shipping facilities. 

b. If a concrete block or brick machine is available, mix and mold about 
100 units as directed by the instructor. It may be necessary to mix and mold 
a few samples, first, in order to get the proper consistency of the mix and to 
understand the operation of the machine. The quantities of materials 
required should be first estimated, the materials procured, the labor gang 
organized, and the concrete block or brick made. If a machine is not avail- 
able, some simple wooden molds (preferably gang molds) can be constructed 
for some concrete brick, and a number of brick made by the wet cast method. 
Care must be taken, during the curing period, to keep the new block and 
brick moist, so that they will not dry out too rapidly. 


JOB 107. LAYING CONCRETE BLOCK WALLS 


The blocks used for concrete walls should be those capable of 
passing the standard specifications for Concrete Building Block 


FIELD WORK 301 


(Appendix 11). The block may be either “load bearing”’ 
“non-load bearing,’’ depending on whether the wall is to support 
a load or not. 

The mortar in concrete block masonry has three functions to 
perform, namely: (1) to form a bed or cushion to take up any 
inequalities in the block surface, and to distribute the pressure 
uniformly; (2) to bind the wall into a solid mass; and (3) to fill 
the spaces and voids between the blocks and keep out the water. 

The mortar used should be a portland cement mortar of a 
1:1,a 1:14, ora 1:2 mix by volume of portland cement and sand 
for load-bearing block, and 1:3 mix for non-load-bearing block. 
The addition of lime to the mortar for load-bearing block, up to 
10 lb. of lime per sack of cement, makes the mortar more plastic 
and workable. Some masons prefer a 1:1:6 mix by volume of 
cement, lime, and sand for non-load-bearing block. 

A mortar batch should be of such size that the entire batch 
will be used within 30 min. after the mixing water is added. 
Retempered mortar should not be used. 

The sand used for the mortar should be clean, durable, 
uncoated, and well graded. No particle of sand should be longer 
than half the thickness of the mortar joint. For 3g-in. mortar 
joints, all sand used in the mortar should pass a No. 8 sieve, and 
not more than 5 per cent should pass a No. 100 seive. 

The thickness of mortar joints in most concrete block masonry 
is 3g in., though variations from !4 in. to 14 in. are common. 

The Patching principles apply to the laying of concrete block: 


1. All block should be thoroughly wet before laying, so that they will 
not absorb the water from the mortar. This wetting is important, but it is 
often neglected. 

2. The block should be laid in a truly horizontal position except i in special 
cases. 

3. The top edge of the block should be laid to a stretched string. 

4. The block masonry should be built in courses perpendicular to the 
pressure it is to bear. 

5. The block in each course should break joints with those in the courses 
immediately above and below so as to provide a good longitudinal bond. 

6. Sufficient transverse bond should be provided when necessary. 

7. All spaces between the bearing parts of the block should be filled with 
mortar. 

8. In laying the ee a layer of mortar should be spread uniformly over 
the bearing surfaces of the last course of block. 


302 CONCRETE PRACTICE 


9. The block should be pressed firmly into this mortar so that some of 
the mortar will be squeezed out. 

10. The vertical joints should be filled with mortar between the adjacent 
surfaces of the blocks. 

11. When blocks are designed to provide a continuous air space in the 
wall, the block and mortar should be so placed that there will not be a con- 
tinuity of concrete and mortar from the outside to the inside surface of the 
wall. 

12. The masonry must be tested frequently with a mason’s level and 
plumb to see that the courses are level and that the wall is plumb. 


When laying concrete block walls, the corners are usually 
first built up for two or three 
courses, and strings are stretched 
from corner to corner (as in brick 
masonry) to aid in the proper lay- 
ing of the block in the courses. 
The joints in concrete block wall 
may be finished in a variety of 
ways. Figure 159 shows several 
of the more common methods of 
pointing. 
After the wall has been built and 
the joints pointed, it should be 
STRUCK RAKED e : 
_ ,  ¢@leaned by brushing or scrubbing. 
Fic. 159.—Methods of pointing 
joints of concrete block walls. When necessary, the wall may be 
washed with a dilute solution of 
commercial hydrochloric acid and water. The wall should after- 
ward be thoroughly rinsed with fresh water to remove all traces 
of the acid. 


STRUCK CONCAVE 


Yi, 


ZL 


Problems.—a. Observe the construction of a concrete block wall, noting 
the size and kind of block, proportions of mortar, thickness of mortar joints, 
method of pointing, laborers used and the duties of each, time required for 
laying the wall, and any items of importance and interest. Compute the 
number of blocks laid per mason per 8-hr. day. How many helpers are there 
per mason? 

b. Construct a concrete block wall as directed by the instructor. First 
estimate the number of blocks required, the amount of cement and sand 
needed for the mortar, and the labor hours required. Then procure the 
block and mortar material and construct the wall, being careful to do good 
work rather than fast work. Compare the actual quantities used with those 
previously estimated. 


SECTION VII 


APPENDICES 


APPENDIX 1 


STANDARD SPECIFICATIONS AND TESTS 
FOR 
PORTLAND CEMENT 
American Society for Testing Materials 
Serial Designation: C 9-21 


These specifications and tests are issued under the fixed designation C 9; 
the final number indicates the year of original adoption as standard, or in 
the case of revision, the year of last revision. 


ApboPTED, 1904; RrevisEep, 1908, 1909, 1916, 1920 (Errective Jan. 1, 1921) 


These specifications were approved Mar. 31, 1922, 
as “American Standard” by the 
American Engineering Standards Committee 


SPECIFICATIONS 


1. Definition. Portland cement is the product obtained by finely pul- 
verizing clinker produced by calcining to incipient fusion an intimate and 
properly proportioned mixture of argillaceous and calcareous materials, 
with no additions subsequent to calcination excepting water and calcined 
or uncalcined gypsum. 


I, CHEMICAL PROPERTIES 
2. Chemical Limits. ‘The following limits shall not be exceeded: 


Per riguition. per conte. 2.., ale .oy2t- 629. 054s a4 4.00 
Pueeale remit. percent... .. 200s ake ss de oes oes 0.85 
Sulfuric anhydride (SO;), per cent. .......24. 0605 600% 2.00 
Renesas MeO). per Cent ie) SiG ete ey A 5.00 


II, PHYSICAL PROPERTIES 
3. Specific Gravity. The specific gravity of cement shall be not less 
than 3.10 (3.07 for white portland cement). Should the test of cement as 
received fall below this requirement, a second test may be made upon an 
303 


304 CONCRETE PRACTICE 


ignited sample. The specific gravity test will not be made unless specifically 
ordered. 

4. Fineness. The residue on a standard No. 200 sieve shall not exceed 
22 per cent by weight. 

5. Soundness. A pat of neat cement shall remain firm and hard, and 
show no signs of distortion, cracking, checking, or disintegration in the 
steam test for soundness. 

6. Time of Setting. The cement shall not develop initial set in less than 
45 min. when the Vicat needle is used, or 60 min. when the Gillmore needle 
is used. Final set shall be attained within 10 hr. 

7. Tensile Strength. The average tensile strength in pounds per square 
inch of not less than three standard mortar briquettes (see Sec. 50) com- 
posed of 1 part cement and 3 parts standard sand, by weight, shall be equal 
to, or higher than, the following: 


Tensile strength, 
Age at test, : 
Storage of briquettes pounds per 
days : 
square inch 
i 1 day in moist air, 6 days in water....... 200 
28 1 day in moist air, 27 days in water...... 300 


8. The average tensile strength of standard mortar at 28 days shall be 
higher than the strength at 7 days. 


III. PACKAGES, MARKING AND STORAGE 


9. Packages and Marking. ‘The cement shall be delivered in suitable 
bags or barrels with the brand and name of the manufacturer plainly marked 
thereon, unless shipped in bulk. <A bag shall contain 94 lb. net. A barrel 
shall contain 376 lb. net. 

10. Storage. ‘The cement shall be stored in such a manner as to permit 
easy access for proper inspection and identification of each shipment, and 
in a suitable weather-tight building which will protect the cement from 
dampness. 

IV. INSPECTION 

11. Inspection. Every facility shall be provided the purchaser for careful 
sampling and inspection at either the mill or at the site of the work, as may 
be specified by the purchaser. At least 10 days from the time of sampling 
shall be allowed for the completion of the 7-day test, and at least 31 days 
shall be allowed for the completion of the 28-day test. The cement shall 
be tested in accordance with the methods hereinafter prescribed. The 
28-day test shall be waived only when specifically so ordered. 


V. REJECTION 


12. Rejection. The cement may be rejected if it fails to meet any of the 
requirements of these specifications. 


APPENDICES 305 


13. Cement shall not be rejected on account of failure to meet the fineness 
requirement if, upon retest after drying at 100°C. for 1 hr., it meets this 
requirement. 

14. Cement failing to meet the test for soundness in steam may be accepted 
if it passes a retest using a new sample at any time within 28 days thereafter. 

15. Packages varying more than 5 per cent from the specified weight 
may be rejected; and if the average weight of packages in any shipment, as 
shown by weighing fifty packages taken at random, is less than that specified, 
the entire shipment may be rejected. 


TESTS 


VI. SAMPLING 


16. Number of Samples. Tests may be made on individual or composite 
samples as may be ordered. Each test sample should weigh at least 8 lb. 

17. (a) Individual Sample.—If{ sampled in cars, one test sample shall be 
taken from each 50 bbl. or fraction thereof. If sampled in bins, one sample 
shall be taken from each 100 bbl. 

(b) Composite Sample.—If sampled in cars, one sample shall be taken from 
one sack in each forty sacks (or 1 bbl. in each 10 bbl.) and combined to form 
one test sample. If sampled in bins or warehouses, one test sample shall 
represent not more than 200 bbl. 

18. Method of Sampling. Cement may be sampled at the mill by any of 
the following methods that may be practicable, as ordered: 

(a) From the Conveyor Delivering to the Bin.—At least 8 lb. of cement shall 
be taken from approximately each 100 bbl. passing over the conveyor. 

(b) From Filled Bins by Means of Proper Sampling Tubes.—Tubes inserted 
vertically may be used for sampling cement to a maximum depth of 10 ft. 
Tubes inserted horizontally may be used where the construction of the bin 
permits. Samples shall be taken from points well distributed over the face 
of the bin. 

(c) From Filled Bins at Points of Discharge.—Sufficient cement shall be 
drawn from the discharge openings to obtain samples representative of the 
cement contained in the bin, as determined by the appearance at the dis- 
charge openings of indicators placed on the surface of the cement directly 
above these openings before drawing of the cement is started. 

19. Treatment of Sample. Samples preferably shall be shipped and 
stored in air-tight containers. Samples shall be passed through a sieve 
having 20 meshes per lin. in. in order thoroughly to mix the sample, break up 
lumps, and remove foreign materials. 


VII. CHEMICAL ANALYSIS 
Loss on IGNITION 
20. Method. One gram of cement shall be heated in a weighed covered 
platinum crucible, of 20 to 25 c.c. capacity, as follows, using either method 
(a) or (b) as ordered: 


306 CONCRETE PRACTICE 


(a) The crucible shall be placed in a hole in an asbestos board, clamped 
horizontally so that about three-fifths of the crucible projects below, and 
blasted at a full red heat for 15 min. with an inclined flame; the loss in weight 
shall be checked by a second blasting for 5 min. Care shall be taken to wipe 
off particles of asbestos that may adhere to the crucible when withdrawn 
from the hole in the board. Greater neatness and shortening of the time of 
heating are secured by making a hole to fit the crucible in a circular disk of 
sheet platinum and placing this disk over a somewhat larger hole in an 
asbestos board. 

(b) The crucible shall be placed in a muffle at any temperature between 
900 and 1000°C. for 15 min., and the loss in weight shall be checked by a 
second heating for 5 min. 

21. Permissible Variation. A permissible variation of 0.25 will be 
allowed, and all results in excess of the specified limit, but within this 
permissible variation, shall be reported as 4 per cent. 


INSOLUBLE RESIDUE 


22. Method. To a 1-g. sample of cement shall be added 10 c.c. of water 
and 5c.c. of concentrated hydrochloric acid; the liquid shall be warmed until 
effervescence ceases. ‘The solution shall be diluted to 50 c.c. and digested 
on a steam bath or hot plate until it is evident that decomposition of the 
cement is complete. The residue shall be filtered, washed with cold water, 
and the filter paper and contents digested in about 30 c.c. of a 5 per cent 
solution of sodium carbonate, the liquid being held at a temperature just 
short of boiling for 15 min. The remaining residue shall be filtered, washed 
with cold water, then with a few drops of hot hydrochloric acid, 1:9, and 
finally with hot water, and then ignited at a red heat and weighed as the 
insoluble residue. 

23. Permissible Variation. A permissible variation of 0.15 will be allowed, 
and all results in excess of the specified limit, but within this permissible 
variation, shall be reported as 0.85 per cent. 


Sutruric ANHYDRIDE 


24. Method. One gram of the cement shall be dissolved in 5 e.c. of 
concentrated hydrochloric acid diluted with 5 ¢.c. of water, with gentle 
warming; when solution is complete, 40 c.c. of water shall be added, the 
solution filtered, and the residue washed thoroughly with water. The solu- 
tion shall be diluted to 250 c.c., heated to boiling, and 10 ¢.c. of a hot 10 per 
cent solution of barium chloride shall be added slowly, drop by drop, from a 
pipette and the boiling continued until the precipitate is well formed. 
The solution shall be digested on the steam bath until the precipitate has 
settled. The precipitate shall be filtered, washed, and the paper and 
contents placed in a weighed platinum crucible and the paper slowly charred 
and consumed without flaming. The barium sulfate shall then be ignited 
and weighed. The weight obtained multiplied by 34.3 gives the percentage 
of sulfuric anhydride. The acid filtrate obtained in the determination of the 
insoluble residue may be used for the estimation of sulfuric anhydride, instead 
of using a separate sample. 


APPENDICES 307 


25. Permissible Variation. A permissible variation of 0.10 will be 
allowed, and all results in excess of the specified limit, but within this 
permissible variation, shall be reported as 2 per cent. 


MAGNESIA 

26. Method. To 0.5 g. of the cement in an evaporating dish shall be 
added 10 c.c. of water to prevent lumping and then 10 ¢.c. of concentrated 
hydrochloric acid. The liquid shall be gently heated and agitated until 
attack is complete. The solution shall then be evaporated to complete 
dryness on a steam or water bath. To hasten dehydration, the residue 
may be heated to 150 or even 200°C. for % to 1 hr. The residue shall be 
treated with 10 c.c. of concentrated hydrochloric acid diluted with an equal 
amount of water. The dish shall be covered and the solution digested for 
10 min. on a steam bath or water bath. The diluted solution shall be 
filtered and the separated silica washed thoroughly with water.! Five cubic 
centimeters of concentrated hydrochloric acid, and sufficient bromine water 
to precipitate any manganese which may be present, shall be added to the 
filtrate (about 250 c.c.). This shall be made alkaline with ammonium 
hydroxide, boiled until there is but a faint odor of ammonia, and the precip- 
itated iron and aluminum hydroxides, after settling, shall be washed with 
hot water, once by decantation and slightly on the filter. Setting aside the 
filtrate, the precipitate shall be transferred by a jet of hot water to the 
precipitating vessel and dissolved in 10 c.c. of hot hydrochloric acid. The 
paper shall be extracted with acid, the solution and washings being added to 
the main solution. The aluminum and iron shall then be reprecipitated at 
boiling heat by ammonium hydroxide and bromine water in a volume of 
about 100 c.c., and the second precipitate shall be collected and washed on the 
filter used in the first instance, if this is still intact. To the combined 
filtrates from the hydroxides of iron and aluminum, reduced in volume if 
need be, 1 c.c. of ammonium hydroxide shall be added, the solution brought 
to boiling, 25 c.c. of a saturated solution of boiling ammonium oxalate 
added, and the boiling continued until the precipitated calcium oxalate has 
assumed a well-defined granular form. ‘The precipitate after 1 hr. shall be 
filtered and washed, then with the filter shall be placed wet in a platinum 
crucible, and the paper burned off over a small flame of a Bunsen burner; 
after ignition it shall be redissolved in hydrochloric acid and thesolution 
diluted to 100 ¢c.c. Ammonia shall be added in slight excess, and the liquid 
boiled. The lime shall then be reprecipitated by ammonium oxalate, 
allowed to stand until settled, filtered, and washed. The combined filtrates 
from the calcium precipitates shall be acidified with hydrochloric acid, 
concentrated on the steam bath to about 150 ¢.c., and made slightly alkaline 
with ammonium hydroxide, boiled and filtered (to remove a little aluminum 
and iron and perhaps calcium). When cool, 10 c.c. of saturated solution of 
sodium-ammonium-hydrogen phosphate shall be added with constant stir- 
ring. When the crystallin ammonium-magnesium orthophosphate has 
formed, ammonia shall be added in moderate excess. The solution shall 


1Since this procedure does not involve the determination of silica, a 
second evaporation is unnecessary. 


308 CONCRETE PRACTICE 


be set aside for several hours in a cool place, filtered and washed with water 
containing 2.5 per cent of NH;. The precipitate shall be dissolved in a 
small quantity of hot hydrochloric acid, the solution diluted to about 100 ¢.c., 
1 c.c. of a saturated solution of sodium-ammonium-hydrogen phosphate 
added, and ammonia drop by drop, with constant stirring, until the precipi- 
tate is again formed as described and the ammonia is in moderate excess. 
The precipitate shall then be allowed to stand about 2 hr., filteredand 
washed as before. The paper and contents shall be placed in a weighed 
platinum crucible, the paper slowly charred, and the resulting carbon 
carefully burned off. The precipitate shall then be ignited to constant 
weight over a Meker burner, or a blast not strong enough to soften or melt 
the pyrophosphate. The weight of magnesium pyrophosphate obtained, 
multiplied by 72.5, gives the percentage of magnesia. The precipitate so 
obtained always contains some calcium and usually small quantities of iron, 
aluminum, and manganese as phosphates. 

27. Permissible Variation. A permissible variation of 0.4 will be allowed, 
and all results in excess of the specified limit, but within this permissible 
variation, shall be reported as 5 per cent. 

VIII. DETERMINATION OF SPECIFIC GRAVITY 

28. Apparatus. The determination of specific gravity shall be made with 
a standardized Le Chatelier apparatus which conforms to the requirements 
illustrated in Fig. 1. This apparatus is standardized by the U. 8. Bureau of 
Standards. Kerosene free from water, or benzine not lighter than 62° 
Baumé, shall be used in making this determination. 

29. Method. The flask shall be filled with either of these liquids to a 
point on the stem between zero and 1 c¢.c., and 64 g. of cement, of thesame 
temperature as the liquid, shall be slowly introduced, taking care that the 
cement does not adhere to the inside of the flask above the liquid and to free 
the cement from air by rolling the flask in an inclined position. After all the 
cement is introduced, the level of the liquid will rise to some division of the 
graduated neck; the difference between readings is the volume displaced by 
64 g. of the cement. 

The specific gravity shall then be obtained from the formula: 

Weight of cement (g.) 
Displaced volume (c.c.) 

30. The flask, during the operation, shall be kept immersed in water, in 
order to avoid variations in the temperature of the liquid in the flask, which 
shall not exceed 0.5°C. The results of repeated tests should agree within 
0.01. 

31. The determination of specific gravity shall be made on the cement as 
received; if it falls below 3.10, a second determination shall be made after 
igniting the sample as described in Sec. 20. 


IX. DETERMINATION OF FINENESS 


32. Apparatus. Wire cloth for standard sieves for cement shall be woven 
(not twilled) from brass, bronze, or other suitable wire, and mounted without 
distortion on frames not less than 114 in. below the top of the frame. The 


Specific gravity = 


APPENDICES 309 


sieve frames shall be circular, approximately 8 in. in diameter, and may be 
provided with a pan and cover. 


a eee 


NNUAL 


» 
% 
Have two @! ec 
Graduations extend 
above land = 
below O Mark --=---.; — — -~ 
| o§ ‘ 
Kw: 
Capacity me: 
of Bulk 
approx. 
25066 «.. S 
dc 
Oost 
Hy ‘ 
ae ie 
[i : 5 ts 
ee es | 


<< 93cm Ct eer eran aca 
Fig. 1.—Le Chatelier apparatus. 


33. A standard No. 200 sieve is one having nominally an 0.0029-in. 
opening and 200 wires per inch standardized by the U. S. Bureau of Stand- 
ards, and conforming to the following requirements: 


310 CONCRETE PRACTICE 


The No. 200 sieve should have 200 wires per in., and the number of wires 
in any whole inch shall not be outside the limits of 192 to 208. No opening 
between adjacent parallel wires shall be more than 0.0050 in. in width. 
The diameter of the wire should be 0.0021 in. and the average diameter shall 
not be outside the limits 0.0019 to 0.0023 in. The value of the sieve, as 
determined by sieving tests made in conformity with the standard specifica- 
tions for these tests on a standardized cement, which gives a residue of 25 to 
20 per cent on the No. 200 sieve, or on other similarly graded material, shall 
not show a variation of more than 1.5 per cent above or below the standards 
maintained at the Bureau of Standards. 

34. Method. ‘The test shall be made with 50 g. of cement. ‘The sieve 
shall be thoroughly clean and dry. The cement shall be placed on the No. 
200 sieve, with pan and cover attached, if desired. ‘The sieve shall be held 
in one hand in a slightly inclined position, so that the sample will be well 
distributed over the sieve, at the same time gently striking the side about 
one hundred and fifty times per minute against the palm of the other hand 
on the up stroke. The sieve shall be turned every twenty-five strokes about 
one-sixth of a revolution in the same direction. The operation shall continue 
until not more than 0.05 g. passes through in 1 min. of continuous sieving. 
The fineness shall be determined from the weight of the residue on the sieve 
expressed as a percentage of the weight of the original sample. 

35. Mechanical sieving devices may be used, but the cement shall not be 
rejected if it meets the fineness requirement when tested by the hand 
method described in See. 34. 


X. MIXING CEMENT PASTES AND MORTARS 


36. Method. The quantity of dry material to be mixed at one time shall 
not exceed 1000 g. nor be less than 500 g. The proportions of cement, 
or cement and sand, shall be stated by weight in grams of the dry materials; 
the quantity of water shall be expressed in cubic centimeters (1 c.c. of 
water = 1 g.). The dry materials shall be weighed, placed upon a non- 
absorbent surface, thoroughly mixed dry if sand is used, and a crater formed 
in the center, into which the proper percentage of clean water shall be 
poured; the material on the outer edge shall be turned into the crater by the 
aid of atrowel. After an interval of 14 min. for the absorption of the water, 
the operation shall be completed by continuous, vigorous mixing, squeezing 
and kneading with the hands for at least 1 min.! During the operation of 
mixing, the hands should be protected by rubber gloves. 

37. The temperature of the room and the mixing water shall be main- 
tained as nearly as practicable at 21°C. (70°F.). 


1 In order to secure uniformity in the results of tests for the time of setting 
and tensile strength, the manner of mixing above described should be care- 
fully followed. At least 1 min. is necessary to obtain the desired plasticity, 
which is not appreciably affected by continuing the mixing for several 
minutes. The exact time necessary is dependent upon the personal equation 
of the operator. The error in mixing should be on the side of overmixing. 


APPENDICES 311 


XI. NORMAL CONSISTENCY 


38. Apparatus. The Vicat apparatus consists of a frame A (Fig. 2) 
bearing a movable rod B, weighing 300 g., one end, C, being 1 cm. in diameter 
for a distance of 6 cm., the other having a removable needle D, 1 mm. in 
diameter, 6 cm. long. The rod is reversible, and can be held in any desired 
position by a screw EH, and has midway between the ends a mark F which 
moves under a scale (graduated to millimeters) attached to the frame A. 


a) 
45 


LI): 
Ith, 
hh 


| ae 
WD) _—=AAZ \\\\\“\\ CAN \\\\ 
co 


| 


11) AN \\\\: A 
TT 


Fig. 2.— Vicat apparatus. 


The paste is held in a conical, hard-rubber ring G, 7 cm. in diameter at the 
base, 4 cm. high, resting on a glass plate H about 10 cm. square. 

39. Method. In making the determination, 500 g. of cement, with a 
measured quantity of water, shall be kneaded into a paste, as described 
in Sec. 36, and quickly formed into a ball with the hands, completing 
the operation by tossing it six times from one hand to the other, maintained 
about 6 in. apart; the ball resting in the palm of one hand shall be pressed into 
the larger end of the rubber ring held in the other hand, completely filling 


312 CONCRETE PRACTICE 


the ring with paste; the excess at the larger end shall then be removed by a 
single movement of the palm of the hand; the ring shall then be placed on its 
larger end on a glass plate, and the excess paste at the smaller end sliced off 
at the top of the ring by a single oblique stroke of a trowel held at a slight 
angle with the top of thering. During these operations, care shall be taken 
not to compress the paste. The paste confined in the ring, resting on the 
plate, shall be placed under the rod, the larger end of which shall be brought 
in contact with the surface of the paste; the scale shall then be read, and the 
rod quickly released. The paste shall be of normal consistency when the 
rod settles to a point 10 mm. below the original surface in 14 min. after being 
released. The apparatus shall be free from all vibrations during the test. 
Trial pastes shall be made with varying percentages of water until the normal 
consistency is obtained. The amount of water required shall be expressed 
in percentage by weight of the dry cement. 

40. The consistency of standard mortar shall depend on the amount of 
water required to produce a paste of normal consistency from the same 
sample of cement. Having determined the normal consistency of the 
sample, the consistency of standard mortar made from the same sample 
shall be as indicated in Table I, the values being in percentage of the com- 
bined dry weights of the cement and standard sand. 

XII DETERMINATION OF SOUNDNESS! 

41. Apparatus. A steam apparatus, which can be maintained at a tempera- 
ture between 98 and 100°C., or one similar to that shown in Fig. 3, is recom- 
mended. The capacity of this apparatus may be increased by using a rack 
for holding the pats in a vertical or inclined position. 

42. Method. A pat from cement paste of normal consistency about 3 in. 
in diameter, 14 in. thick at the center, and tapering to a thin edge, shall be © 
made on clean glass plates about 4 in. square, and stored in moist air for 
24 hr. In molding the pat, the cement paste shall first be flattened on the 
glass and the pat when formed by drawing the trowel from the outer edge 
toward the center. 

43. The pat shall then be placed in an atmosphere of steam at a tempera- 
ture between 98 and 100°C. upon a suitable support 1 in. above boiling water 
for 5 hr, 

44, Should the pat leave the plate, distortion may be detected best with a 
straight edge applied to the surface which was in contact with the plate. 


XIII. DETERMINATION OF TIME OF SETTING 

45. The following are alternate methods, either of which may be used as 
ordered: 

1 Unsoundness is usually manifested by change in volume which causes 
distortion, cracking, checking or disintegration. 

Pats improperly made or exposed to drying may develop what are known 
as shrinkage cracks within the first 24 hr. and are not an indication of 
unsoundness. These conditions are illustrated in Fig. 4. 

The failure of the pats to remain on the glass or the cracking of the glass to 
which the pats are attached does not necessarily indicate unsoundness. 


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APPENDICES 


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CONCRETE PRACTICE 


314 


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APPENDICES 315 
46. Vicat Apparatus. The time of setting shall be determined with the 
Vicat apparatus described in Sec. 38. (See Fig. 2.) 


TaBLE I.—PEROCENTAGE OF WATER FOR STANDARD MorTARS 
i 


Percentage of Percentage of Percentage of Percentage of 
water for neat water for one water for neat water for one 
cement paste of cement, three cement paste of cement, three 
normal consist- | standard Ottawa || normal consist- | standard Ottawa 

ency sand ency sand 

15 9.0 23 10.3 

16 9.2 24 10.5 

17 9.3 25 Sieg 

18 9.5 26 10.8 

19 9.7 27 11.0 

20 9.8 28 11.2 

21 10.0 29 nD em 

22 1022 30 Le 


47. Vicat Method. A paste of normal consistency shall be molded in the 
hard-rubber ring G as described in Sec. 39, and placed under the rod B, 
the smaller end of which shall then be carefully brought in contact with the 
surface of the paste, and the rod quickly released. The initial set shall be 
said to have occurred when the needle ceases to pass a point 5 mm. above the 
glass plate in 14 min. after being released; and the final set, when the needle 
does not sink visibly into the paste. The test pieces shall be kept in moist 
air during the test. This may be accomplished by placing them on a rack 
over water contained in a pan and covered by a damp cloth, kept from 
contact with them by means of a wire screen; or they may be stored in a 
moist closet. Care shall be taken to keep the needle clean, as the collection 
of cement on the sides of the needle retards the penetration, while cement on 
the point may increase the penetration. The time of setting is affected not 
only by the percentage and temperature of the water used and the amount 
of kneading the paste receives, but by the temperature and humidity of the 
air, and its determination is therefore only approximate. 

48. Gillmore Needles. The time of setting shall be determined by the 
Gillmore needles. The Gillmore needles should preferably be mounted as 
shown in Fig. 5 (b). 

49. Gillmore Method. The time of setting shall be determined as follows: 
A pat of neat cement paste about 3 in. in diameter and 4 in. in thickness 
with a flat top (Fig. 5 (a)) mixed to a normal consistency, shall be kept 
in moist air at a temperature maintained as nearly as practicable at 21°C. 
(70°F.). The cement shall be considered to have acquired its initial set 
when the pat will bear, without appreciable indentation, the Gillmore 
needle, 14 in. in diameter, loaded to weigh 44 lb. The final set has been 
acquired when the pat will bear without appreciable indentation, the Gill- 


316 CONCRETE PRACTICE 


more needle 144 in. in diameter, loaded to weigh 1 lb. In making the test, 
the needles shall be held in a vertical position and applied lightly to the 
surface of the pat. 


XIV. TENSION TESTS 


50. Form of Test Piece. The form of test piece shown in Fig. 6 shall be 
used. The molds shall be made of non-corroding metal and have sufficient 
material in the sides to prevent spreading during molding. Gang molds 


(a) Pat with top surface flattened for determining time by Gillmore method. 
ee. 


Z 


(b) Gillmore needles. 
Fire: 5. 


when used shall be of the type shown in Fig. 7. Molds shall be wiped with 
an oily cloth before using. 

51. Standard Sand. The sand to be used shall be natural sand from 
Ottawa, IIl., screened to pass a No. 20 sieve and retained on a No. 30 sieve. 
This sand may be obtained from the Ottawa Silica Co., at a cost of 3 ets. 
per lb., f.o.b. cars, Ottawa, Ill. 

52. This sand, having passed the No. 20 sieve, shall be considered stand- 
ard when not more than 5 g. passes the No. 30 sieve after 1 min. continuous 
sieving of a 500-g. sample. 

53. The sieves shall conform to the following specifications: 


APPENDICES 317 


Fig. 7.—Gang mold. 


318 CONCRETE PRACTICE 


The No. 20 sieve shall have between 19.5 and 20.5 wires per whole inch 
of the warp wires and between 19 and 21 wires per whole inch of the shoot 
wires. The diameter of the wire should be 0.0165 in. and the average diam- 
eter shall not be outside the limits of 0.0160 and 0.0170 in. 

The No. 30 sieve shall have between 29.5 and 30.5 wires per whole inch 
of the warp wires and between 28.5 and 31.5 wires per whole inch of the 
shoot wires. The diameter of the wire should be 0.0110 in. and the aver- 
age diameter shall not be outside the limits 0.0105 to 0.0115 in. 

54. Molding. Immediately after mixing, the standard mortar shall be 
placed in the molds, pressed in firmly with the thumbs and smoothed off 
with a trowel without ramming. Additional mortar shall be heaped above 
the mold and smoothed off with a trowel; the trowel shall be drawn over 
the mold in such a manner as to exert a moderate pressure on the material. 
The mold shall then be turned over and the operation of heaping, thumbing, 
and smoothing off repeated. 

55. Testing. Tests shall be made with any standard machine. The 
briquettes shall be tested as soon as they are removed from the water. The 
bearing surfaces of the clips and briquettes shall be free from grains of sand 
or dirt. The briqeuttes shall be carefully centered and the load applied 
continuously at the rate of 600 lb. per min. 

56. Testing machines should be frequently calibrated in order to deter- 
mine their accuracy. 

57. Faulty Briquettes. Briquettes that are manifestly faulty, or that 
give strengths differing more than 15 per cent from the average value of all 
test pieces made from the same sample and broken at the same period, shall 
not be considered in determining the tensile strength. 


XV. STORAGE OF TEST PIECES 


58. Apparatus. The moist closet may consist of a soapstone, slate, or 
concrete box, or a wooden box lined with metal. If a wooden box is used, 
the interior should be covered with felt or broad wicking kept wet. The 
bottom of the moist closet should be covered with water. The interior 
of the closet should be provided with non-abosrbent shelves on which to 
place the test pieces, the shelves being so arranged that they may be with- 
drawn readily. 

59. Methods. Unless otherwise specified, all test pieces, immediately 
after molding, shall be placed in the moist closet for from 20 to 24 hr. 

60. The briquettes shall be kept in molds on glass plates in the moist 
closet for at least 20 hr. After from 20 to 24 hr. in moist air the briquettes 
shall be immersed in clean water in storage tanks of non-corroding material. 

61. The air and water shall be maintained as nearly as practicable at a 
temperature of 21°C, (70°F.). 


APPENDICES 319 
APPENDIX 2 


STANDARD METHOD OF TEST 
_ FOR 
UNIT WEIGHT OF AGGREGATE FOR CONCRETE 
American Society for Testing Materials 
Serial Designation: C 29-21 


This method is issued under the fixed designation C 29; the final number 
indicates the year of original adoption as standard, or, in the case of revi- 
sion, the year of last revision. 


PROPOSED AS TENTATIVE, 1920; ApoprEep, 1921 


This method was approved May 29, 1923, 
as “Tentative American Standard” by the 
American Engineering Standards Committee 


1. The unit weight of fine, coarse, or mixed aggregates for concrete shall 
be determined by the following method: 

2. Apparatus. (a) The apparatus required consists of a cylindrical metal 
measure, a tamping rod, and a scale or balance, sensitive to 0.5 per cent of 
the weight of the sample to be weighed. 

(b) Measures.—The measure shall be of metal, preferably machined 
to accurate dimensions on the inside, cylindrical in form, water-tight, and 
of sufficient rigidity to retain its form under rough usage, with top and 
bottom true and even, and preferably provided with handles. 

The measure shall be of }40-, 4-, or 1-cu. ft. capacity, depending on 
the maximum diameter of the coarsest particles in the aggregate, and shall 
be of the following dimensions: 


: Inside Inside Minimum thick- | Diameter of lar- 
bapacity, diameter, | height, ness of metal, gest particles of 
A inches inches U. S. Gage aggregate, inches 

V9 6 6.10 No. 11 Under 4 
Vy 10 11.00° No. 8 Under 144 
1 14 11.23 No, “5” Over 144 


(c) Tamping Rod.—The tamping rod shall be a straight metal rod 34 in. 
in diameter and 18 in. long, with one end tapered for a distance of 1 in. to a 
blunt bullet-shaped point. 


320 CONCRETE PRACTICE 


3. Calibrating the Measure. The measure shall be calibrated by accu- 
rately determining the weight of water at 16.7°C. (62°F.) required to fill it. 
The factor for any unit shall be obtained by dividing the unit weight of 
water at 16.7°C. (62°F.)! by the weight of water at 16.7°C. (62°F.) required 
to fill the measure. 

4. The sample of aggregate shall be room dry and thoroughly mixed. 

5. Method. (a) The measure shall be filled one-third full and the top 
leveled off with the fingers. The mass shall be tamped with the pointed 
end of the tamping rod twenty-five times, evenly distributed over the sur- 
face. The measure shall be filled two-thirds full and again tamped twenty- 
five times as before. The measure shall then be filled to overflowing, 
tamped twenty-five times, and the surplus aggregate struck off, using the 
tamping rod as a straightedge. 

In tamping the first layer the rod should not be permitted forcibly to 
strike the bottom of the measure. In tamping the second and final layers, 
only enough force to cause the tamping rod to penetrate the last layer of 
aggregate placed in the measure should be used. No effort should be made 
to fill holes left by the rod when the aggregate is damp. 

(b) The net weight of the aggregate in the measure shall be determined. 
The unit weight of the aggregate shall then be obtained by multiplying the 
net weight of the aggregate by the factor found as described in Sec. 3. 

6. Accuracy. Results with the same sample should check within 1 per 
cent. 


APPENDIX 3 


STANDARD METHOD OF TEST 
FOR 
SIEVE ANALYSIS OF AGGREGATES FOR CONCRETE 
American Society for Testing Materials 
Serial Designation: C 41-24 


This method is issued under the fixed designation C 41; the final number 
indicates the year of original adoption as standard or, in the case of revision, 
the year of last revision. 


IssumD as TENTATIVE, 1921; ApopTED, 1922; REvIsED, 1924 


1. Sampling. A representative test sample of the aggregate shall be 
selected by quartering or by use of a sampler, which after drying will give 
not less than the following: 

(a) Fine aggregate, 500 g. 

(b) Coarse aggregate, or a mixture of fine and coarse aggregates, weight 
in grams, 3000 times size of largest sieve required, measured in inches. 


1 The unit weight of water at 16.7°C. (62°F.) is 62.355 Ib. per cu. ft. _ ; 


APPENDICES 321 


TABLE | 
ert ea 
Sieve Wire Tol ' 
: : olerance, per cen 
_ Opening diameter »P 
Sieve number! 
or Aver- f Maxi- 
Bia nt Wire diameter 
size in inches age 
Mm. Jere TG Berea bee 8 
OPeRs) a saute Open 


ing | Under | Over | ing 


| | | 


No. 100 0.1490 .0059,0. 102 0.0040 6 15 35 40 
No. 50 0.297,0.0117|0.188 0.0074 6 15 35 40 
No. 30 0.59 |0.02320.33 |0.0130 5 15 30 25 
No 16 1.19 |0.0469,0.54 |0.0213 3 15 30 10 
No. 8 2.38 |0.0937/0.84 |0.0331 3 15 30 10 
Nor 4 4.76 |0.187 {1.27 |0.050 3 15 30 10 

3¢ in. 9.5 |0.375 |2.33 |0.092 3 10 10 10 

24 in, 19.0 (0.75 (3.42 |0.135 3 10 10 10 
to doin, 20.4 {1.00 |4.12 |0.162 3 10 10 10 
14 in. 38.0 {1.50 [4.50 |0.177 3 10 10 10 
east 50.8 |2.00 /|4.88 |0.192 3 10 10 10 
3. in. 7.0 |3.00 (6.3 |0.25 3 10 10 10 


1 The requirements for sieves No. 100 to No. 4 conform to the requirements of the U. S 
Standard Sieve Series as given in U. S. Bureau of Standards Letter Circular No. 74. The 
liberal tolerances will permit the use of certain sieves which do not exactly correspond to the 
numbers given in table. 


2. Treatment of Sample. The sample shall be dried at not over 110°C. 
(230°F.) to constant weight. 

3. Sieves. (a) The sieves shall be of square mesh wire cloth and shall be 
mounted on substantial frames constructed in a manner that will prevent 
loss of material during sifting. 

(b) The size of wire and sieve openings shall be as given in Table I. 

4. Procedure. (a) The sample shall be separated into a series of sizes by 
means of the sieves specified in Sec. 3. Sifting shall be continued until 
not more than 1 per cent by weight of the sample passes any sieve during 
1 min. 

(b) Each size shall be weighed on a balance or scale which is sensitive to 
1/000 of the weight of the test sample. 

(c) The percentage by weight of the total sample which is finer than each 
of the sieves shall be computed. 

5. Report. (a) The percentages in sieve analysis shall be reported to the 
nearest whole number. 

(b) If more than 15 per cent of a fine aggregate is coarser than the No. 4 
sieve, or more than 15 per cent of a coarse aggregate is finer than the No. 4 
sieve, the sieve analysis of the portions finer and coarser than this sieve shall 
be reported separately. 


322 CONCRETE PRACTICE 


APPENDIX 4 


TENTATIVE METHOD OF DECANTATION TEST 
FOR 
SAND AND OTHER FINE AGGREGATES 
American Society for Testing Materials 
Serial Designation: D 136-22 T 


This is a Tentative Standard only, published for the purpose of eliciting 
criticism and suggestions. It is not a Standard of the Society and until its 
adoption as Standard it is subject to revision. 


IssuED, 1922 


1. Scope. This method of test covers the determination of the total 
quantity of silt, loam, clay, etc., in sand and other fine aggregates. ! 

2. Apparatus. The pan or vessel to be used in the determination shall be ° 
approximately 9 in. (230 mm.) in diameter and not less than 4 in. (102 mm.) 
in depth. 

3. Treatment of Sample. The sample must contain sufficient moisture 
to prevent segregation and shall be thoroughly mixed. A representative 
portion of the sample sufficient to yield approximately 500 g. of dried 
material, shall then be dried to a constant weight at a temperature not 
exceeding 110°C. (230°F.). 

4. Procedure. The dried material shall be placed in the pan and sufficient 
water added to cover the sample (about 225 ¢.c.). The contents of the pan 
shall be agitated vigorously for 15 sec., and then be allowed to settle for 15 
sec., after which the water shall be poured off, care being taken not to pour 
off any sand. This operation shall be repeated until the wash water is 
clear. Asa precaution, the wash water shall be poured through a 200-mesh 
sieve and any material retained thereon returned to the washed sample. 
The washed sand shall be dried to a constant weight at a temperature not 
exceeding 110°C.. (230°F.) and weighed. 

5. Calculation of Results. The results shall be calculated from the 
formula: 

Percentage of silt, clay, loam, etc. = 
original dry weight —weight after washing 
original dry weight 

6. Check Determination. When check determinations are desired, the 
wash water shall be evaporated to dryness, the residue weighed, and the 
percentage calculated from the formula: 


x 100 


weight of residue 
original dry weight 
1 This determination of the percentage of silt, clay, loam, etc., will include 
all water-soluble material present, the percentage of which may be deter- 
mined separately if desired. 


Percentage of silt, loam, clay, etc. = x 100 


APPEN DICES 323 


APPENDIX 5 


STANDARD METHOD OF TEST 
FOR 
ORGANIC IMPURITIES IN SANDS FOR CONCRETE 
American Society for Testing Materials 
Serial Designation: C 40-22 


This method is issued under the fixed designation C 40; the final number 
indicates the year of original adoption as standard, or in the case of revision, 
the year of last revision. 


PROPOSED AS TENTATIVE, 1921; ApopTED, 1922 


This method was approved May 29, 1923, 
as “Tentative American Standard” by the 
American Engineering Standards Committee. 


1. Scope. The test herein specified is an approximate test for the presence 
of injurious organic compounds in natural sands for cement mortar or 
concrete. The principal value of the test is in furnishing a warning that 
further tests of the sand are necessary before they be used in concrete. 
Sands which produce a color in the sodium hydroxide solution darker than 
the standard color should be subjected to strength tests in mortar or con- 
crete before use. 

2. Sample. (a) A representative test sample of sand of about 1 lb. shall 
be obtained by quartering or by the use of a sampler. 

Procedure. (b) A 12-0z. graduated glass prescription bottle shall be filled 
to the 414-0z. mark with the sand to be tested. 

(c) A 3 per cent solution of sodium hydroxide (NaOH) in water shall be 
added until the volume of sand and liquid after shaking gives a total value 
of 7 liquid oz. 

(d) The bottle shall be stoppered and shaken thoroughly and then allowed 
to stand for 24 hr. 

(e) A standard color solution shall be prepared by adding 2.5 c.c. of a 2 
per cent solution of tannic acid in 10 per cent alcohol to 22.5 ¢.c. of a 3 per 
cent sodium hydroxide solution. This shall be placed in a 12-oz. prescription 
bottle, stoppered and allowed to stand for 24 hr., then 25 c.c. of water added. 

Color Value. (f) The color of the clear liquid above the sand shall be 
compared with the standard color solution prepared as in Paragraph (e) 
or with a glass of color similar to the standard solution. 

3. Solutions darker in color than the standard color have a “‘color value”’ 
higher than 250 parts per million in terms of tannic acid. 


324 CONCRETE PRACTICE 


APPENDIX 6 


PROPORTIONS! FOR CONCRETE OF GIVEN COMPRESSIVE 
STRENGTH AT 28 DAYS 


From the 1924 Report of the Joint Committee on Standard Specifications 
for Concrete and Reinforced Concrete. : 

The table gives the proportions in which portland cement and a wide range 
in sizes of fine and coarse aggregates should be mixed to obtain concrete of 
compressive strengths ranging from 1500 to 3000 Ib. per sq. in. at 28 days. 
Proportions are given for concrete of four different consistencies. 

The purpose of the table is twofold: 

(1) To furnish a guide in the selection of mixtures to be used in preliminary 
investigations of the strength of concrete from given materials. 

(2) To indicate proportions which may be expected to produce concrete of 
a given strength under average conditions where control tests are not made. 

If the proportions to be used in the work are selected from the table with- 
out preliminary tests of the materials, and control tests are not made during 
the progress of the work, the mixtures in bold-face type shall be used. 

The use of this table as a guide in the selection of concrete mixtures is 
based on the following: 

(1) Concrete shall be plastic; 

(2) Aggregates shall be clean and structurally sound; 

(3) Aggregates shall be graded between the sizes indicated; 

(4) Cement shall conform to the requirements of the Standard Specifica- 
tions and Tests for Portland Cement (Serial Designation: C 9-21) of the 
American Society for Testing Materials. (Appendix 1.) 

The plasticity of the concrete shall be determined by the slump test 
carried out in accordance with the Tentative Method of Test for Consistency 
of Portland-Cement Concrete (Serial Designation: D 1388-25 T) of the 
American Society for Testing Materials. (Appendix 7.) 

Apply the following rules in determining the size assigned to a given 
aggregate: 

(1) Not less than 15 per cent shall be retained between the sieve which is 
considered the maximum size? and the next smaller sieve. 

(2) Not more than 15 per cent of a coarse aggregate shall be finer than the 
sieve considered as the minimum size.? 

(3) Only the sieve sizes given in the table shall be considered in applying 
Rules 1 and 2. 


1 Based on the 28-day compressive strengths of 6- by 12-in. cylinders, made 
and stored in accordance with the Standard Methods of Making Compression 
Tests of Concrete (Serial Designation: C 39-25) of the American Society 
for Testing Materials. (Appendix 8.) 

2 For example: a graded sand with 16 per cent retained on the No. 8 sieve 
would fall in the 0-No. 4 size; if 14 per cent or less were retained, the sand 
would fall in the 0-No. 8 size. A coarse aggregate having 16 per cent 
coarser than 2-in. sieve would be considered as 3-in. aggregate. 


325 


APPENDICES 


(4) Sieve analysis shall be made in accordance with the Standard Method 


of Test for Sieve Analysis of Aggregates for Concrete (Serial Designation: 


C 41-24) of the American Society for Testing Materials. 


(Appendix 3. ) 


Proportions may be interpolated for concrete strengths, aggregate sizes 


and consistencies not covered by the table or determined by test. 


PROPORTIONS FOR 1500 Ls. PER Sq. IN. CONCRETE 


Fine 


Proportions are expressed by volume as follows: Portland Cement: 


Aggregate: Coarse Aggregate. 


Thus 1:2.6:4.6 indicates 1 part by volume of portland cement, 2.6 parts 


by volume of fine aggregate, and 4.6 parts by volume of coarse aggregate. 


Size of fine aggregate 


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Size of coarse 
aggregate 


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419619 Onda OAD 110 B= 00 haw Oran Rand TROD 0 0 19 15 115 1 +H 018 19 +H 
5 wi gg A THON tog ose od od ed 4 SHA dian vod ed 1 sO O03. 19 eg 
ONON RHWhm HOyr COOH DOWD MHOS HOODOO OtRD ODAWH QANHAO 
Osos IN THN 19.19 gyi od O19 09 siieg CN 10 wi gio Sid gid vivied ol 1919 ios SAB OS 
HOOR OHOn ID HO 12 O en 19 mRO AOR Dm 0 Anwor Roan OGdH OOnn 
Sod eg oo ogy ooo OS eg CoN ed OO g ogc 0903 vind wise st seg CN 
HOMH Oth OD DAMN DHOH DMON WOAH NHONM HOMHR OCHM+ OMA 
HOE HHA WH CGSwd staan 1519 sod Cid god DER O19 qos O18 09 
00 09 «© 00 HO 6919 chat Thom OH 0g Orato IQ AWS sO O19 HOOD roared Sie) Oth 
oo od ed CON ONAG CNA ANd od 03 ed 4 05 03 ed 4 co Ned woo ei ioe oc > a 
Seas lh a as snare eewae eet eived ot ace et 4 eel aie el Aged St aet heb ots 
COM NINWO ANNAN WHOM BORD NAAN COON MHOSG BNOH AMA 
woo eg 19 Hed 19.15 si os COIs Steg 19 19 gi od O15 gi od 15 i gi od C19 giod O18 09 
0 EY AOOH Ran ODOR OOS Hoa aha ODOM oONIet Oats COWS 
OANA NAAN AA Aad Ade Colo Bal ON CONT Coie Bal od oo ga 0303 ei 
Seeeate seer ea eli rear el ied ean a eee et eal tell Se i ae a dil ities 
DOWD ONAR CHM ANAHDH ANIM WAMN COON t1HOO nes cdr 
visio a HEI OG xi od OOH 09 19 Hed 19.19 i od O19 gis 1D Ht god Ord ios S18 09 
0 =H +H od HHO HOOD NOD OH 09 DHaN 900.0 AO 19 NO Anas 
Acid AA ei ANd ANd Ando ANd AA AA eo OO NEI od ON ed 4 Ned 
MHhRO FAHRO AHRO AHthO AHRO FHHRO AHRO FAHRO FHHRO FAHRO FAHhO 
re re re re re re re re res re 5 mal 
OOO 6! OOF CLIO GC OHO CO Om C1O1O 0 FOC OOM CIO O10) O'O CIO ClO OO OOToLOm moloLonS 
PeperPryp PYPHSH HHH YPHHH YHHH HHH YHHHH BHHH HHH HPHHH HYHHH 
\ OC EDO \ANMO \a Ka \aen Amen co Ane O00 \NODCOOD LOD COO 
\Red O00 0 Leon SA co \NeDOO AMO 9 0 lS co AS ‘S \S 
Nace rN OLS OS 
4 . As! . . . . 
- qi Na (=| . . . . . 
>» aN = : & ; A : : 
: et my nN q An a Aa =| q 
a 3° ° ° ° om =N - rv = o=t 
5 ae = a “= a a) Nn saa) N A) 
© ~ x = =e ° ° re) re) fo) } 
8 3 3 3 3 = = r. ie = is 
“oo Noo \oo Nxt \st \ 
Z Z Zi a a oN oN oN oN oN oN 


CONCRETE PRACTICE 


326 


PROPORTIONS FOR 2000 Ls. PER Sq. IN. CONCRETE 


Fine 


Proportions are expressed by volume as follows: Portland Cement 


Aggregate: Coarse Aggregate. 


Thus 1:2.6:4.6 indicates 1 part by volume of portland cement, 2.6 parts 
by volume of fine aggregate, and 4.6 parts by volume of coarse aggregate. 


Size of fine aggregate 


Slump, 
inches 


Size of coarse 
aggregate 


OHO ONES HOM ONAD HHO Abie? VtOQNH |MOH MOWMD CASO 
NAA SHAAN WAN WAN Sad voGN wWriega OIA wviega 1D Hi gi od 
IQR COMM HHH ANON ORS DQAWH Kas Bann Honw mane niet 
SIH SGM CNA HN ANi HMA MOA HN woe woes toed 
Seas AeA sea Seer rat onl od waist eal yal wtted ea ett mt net ont ted ted Ray ae ow 
HON BDQArA OOMAH CHMR OWHWO OCOMHT HHAR ACON OCNMONM DBRHAAOS 
CONE GOAN WHAN WGN THAN WN WA wea Noh El 19.19 sfiod 
INOMD COMN OHO NMHthO HOMO OH ORIC9 ANOn oman CO AHS Or 6919 O09 
OOAA GAnid AA ANd ANTiO NAG one OAc Od cocoa 09 03 ed 
tried bo I oe oe he So Do reread rie et aoe et et wad sel welt rol ed hte miei etee ol peti so 
INrIBH AROMW AAW HOHO ACON Hatt HMARR HWOUN BtRO ANAS 
Hg WOON WHA Widdion won WHA wie WOON wwiedal 19.19 od 
SOOM SARS BHMS HOWH BOA DHOn OtRH SAS HOU AOC AN Oo 
ON ANeid Addin ANOS ANdidic ANd Addo AN OA ONES c3 ON ed 4 
aoa area bs oo a sree viet ha ee wi ted et vl ld ot Reet pas dain ariel 
RANOQD MHAN AMNWQ MOHAR ANON WBAWMD NHRA MoNn AORN ANAS 
HH VAN HHA WisgGa wOaN WA wea WAN WHA wis gies 
ONERH NAWA NOHO Frm Bad 6WHAwod WHAMS HOWD aon 00 Oth 
ANed Addo Addo Addo Gai ANd Addi Addis ANd ANd ANS 
aoaded sea AeA reac Ase ated ot Seed wt ied et ied et eet dot wot pol pot 
DHQmA MAAN SHIH HOUMA HOAN AMM OHNOAR MOAM ANOKO CHA 
HMI WAN WHgN WidGN THAN THAN Wr gia TOAN Wan Sogn 
NRWO HNHH QONK ASAm KNHOS ASWA Aawa Anew SONOS BHHOS HWS 
Added Ando Patio HiniS rds Adi Aridio Addo AA ANd AA 
eee Sea Area 5 oo oe aeewae Sey pol al wel ed mt el at al vol eat el ok al ol iil 
APO HPO AMES AWE O NRO EO Ath ARO MRO MYR rin > 
° 200 2° 
S828 2882 S388 S858 SESS S382 S288 BESS SESS BESS SESE 
WNODEOW  \NODDO OC NM O CO \NMOCW WOO OCO \NMDOCO MMOH \NODOW \NMDOCW \NMOC NOOO 
28 ae PN aN a 2 aS ae 


None.... 


No. 4 to 34 in.. 


No. 4 to lin... 


No. 4 to 134 in. 


No. 4 t0\2:ine.. 


$2 to Lin... 


3g to l}gin.... 


Se to. 2: ines oe 


$4 to 132 in.. 


34. to 2 in. ss... 


$4 to'3. in. 


Ni che 5 
3 
laa) A 5. 
a © 
a oa 
& 35° 
ica) o q 
Ei Cress 
es wd 

OSs Se 
iS, o) & 
. a 
Z, me 
ee ° 
— mM fe, 
: a 
g2% 
rom o 
mS a = ¢g 
w & op) Lass} 
5 cae ta 
S : © 5S 
Se ay go Mea 
IS Zz A 
a yee. 
A ie ie ee 
= N et a 
ee ied 
Cin ee ee 
es Z & § 
2 oo 
0 O 
SO & Weg 
e $< 8 
° 2 Ro 
oy pas) as 
fe) a 
. a oe 
q © 
mM 6c a 
5, ere 
5.8 = 
& 8 5 

oO oO 
Bes Bes 

Ay. SBE 

< 


by volume of fine aggregate, and 4.6 parts by volume of coarse aggregate. 


Size of fine aggregate 


s 
\oo 
=. 
oOo 
= 
re) 
a 
ro) 
CO 
3 
Z 
roo) 
+ 
re 
fe) 
Z 
ro) 
(o.6) 
N 
fe) 
a 
° 

a2 

sel 
aS 
em 


Size of coarse 
aggregate 


} 
} 
} 
} 
- 
} 
} 


less Tle eee {ee TC uee—_—_ i Tr i er nr OTe eer — Tee ees NS 
d ; A 5 : ; : ; 
—_ q q . . . . 
Ae —_ be = e qd a qa Fy 
= 3 “ x F & E te E 2 
. [o} fe) [e) fe) om bi, -_ St m _ Coal 
i © os a 2 co) qo A = i) aa) 
© ~ Bi a } ° ° } } ° 
i=} . A . : a=) 
E S S S S o ae ie es = . 
iz Z Zz a Zi on EN on on oN oN 


CONCRETE PRACTICE 


328 


CONCRETE 


PER Sq. IN. 


Proportions FOR 3000 Lp. 


Proportions are expressed by volume as follows: Portland Cement: Fine 


Aggregate: Coarse Aggregate. 


Thus 1:2.6:4.6 indicates 1 part by volume of portland cement, 2.6 parts by 


volume of fine aggregate, and 4.6 parts by volume of coarse aggregate. 


Size of fine aggregate 


| 

- 

- 

s 

fe) 

= 

o 

lo) 

eC) 

mn 

o 

st 

bs | 

fe} 

a 

j=) 

ie.) 

N 

fe} 

a 

So 
28 
S5 
ae 


Size of coarse 
aggregate 


INONE:....- 


No. 4 to 34 in.. 


No; 4 toil in... 


No. 4 to 14 in. 


No. 4 to 2.1n7).. 


36 to lin... 


3g to 1}4 in.... 


34 to 2in... 


$4 to-2 in... 


34) toroid eaeneys 


APPENDICES ; o29 


APPENDIX 7 


TENTATIVE METHOD OF TEST 
FOR 
CONSISTENCY OF PORTLAND CEMENT CONCRETE 
American Society for Testing Materials 
Serial Designation: D 138-25 T 


This is a Tentative Standard only, published for the purpose of eliciting 
criticism and suggestions. It is not a Standard of the Society and until its 


adoption as Standard it is subject to revision. 
IssuED, 1922; Revisep 1925 


1. Scope. This test covers the method to be used both in the laboratory 
and in the field for determining consistency of concrete.} 


Lop rep 3 pa ee eee Pa Go cel ee 
«es Elevation. " 


Las xe 
st ae ee 
~ By st 
ny aN 
ly y 


1 This test is not considered applicable when there is a considerable amount 
of coarse aggregate over 2 in. in size in the concrete. The committee is 
now working on a method suitable for determining the consistency of con- 


crete using aggregate over 2 in, in size. 


330 CONCRETE PRACTICE 


2. Apparatus. The test specimen shall be formed in a mold of No. 16 
gage galvanized metal in the form of the lateral surface of the frustrum of 
a cone with the base 8 in. in diameter, the upper surface 4 in. in diameter, 
and the altitude 12 in. The base and the top shall be open and parallel 
to each other and at right angles to the axis of the cone. The mold shall be 
provided with foot pieces and handles as shown in Fig. 1. 

3. Sample. When the test is made at the mixer, the sample shall be taken 
from the pile of concrete immediately after the entire batch has been dis- 
charged. When testing concrete that has been hauled from a central mix- 
ing plant, the sample shall be taken from the concrete immediately after 
it has been dumped on the subgrade. 

4. Procedure. The mold shall be placed on a flat, non-absorbent surface, 
such as a smooth plank or a slab of concrete, and the operator shall hold the 
form firmly in place, while it is being filled, by standing on the foot pieces. 
The mold shall be filled to about one-fourth of its height with the concrete 
which shall then be puddled, using 20 to 30 strokes of a %-in. rod pointed 
at the lower end. The filling shall be completed in successive layers similar 
to the first and the top struck off so that the mold is exactly filled. The 
mold shall then be removed by being raised vertically, immediately after 
being filled. The molded concrete shall then be allowed to subside, until 
quiescent, and the height of the specimen measured. 

5. Slump. The consistency shall be recorded in terms of inches of sub- 
sidence of the specimen during the test, which shall be known as the slump. 


Slump = 12 — inches of height after subsidence 


APPENDIX 8 


STANDARD METHODS 
OF 
MAKING COMPRESSION TESTS OF CONCRETE 
American Society for Testing Materials 
Serial Designation: C 39-25 


These methods are issued under the fixed designation C 39; the final 
number indicates the year of original adoption as standard or, in the case 
of revision, the year of last revision. 


PROPOSED AS TENTATIVE, 1921; ApopTED, 1925 


1. Scope. These methods are intended to cover compression tests of con- 
crete made in a laboratory where accurate control of quantities of materials 
and test conditions is possible. They are designed to apply primarily to 
hand-mixed concrete. ‘These methods may be used with slight modifica- 
tion in making tests of concrete for wearing resistance, bond between con- 


APPENDICES dol 


crete and steel, impermeability, etc. The investigation of machine-mixed 
concrete will require certain obvious changes in the method. For methods 
of conducting compression tests of concrete specimens made during the 
progress of construction work, see the Standard Methods of Making and 
Storing Specimens of Concrete in the Field (Serial Designation: C 31) of 
the American Society for Testing Materials.1 

2. Preparation of Materials. Materials shall be brought to room tem- 
peratures (65 to 75°F.) before beginning tests. Cement shall be stored in 
a dry place; preferably in covered metal cans. The cement shall be thor- 
oughly mixed in advance, in order that the sample may be uniform through- 
out the tests. It shall be sifted through a No. 16 sieve and all lumps 
rejected. Aggregates shall be in a room-dry condition when used in con- 
crete tests. In general, aggregates should be separated on the No. 4, 3<-in. 
and 114-in. sieves? and recombined to the average original sieve analysis 
for each batch. Fine aggregate should be separated into different sizes also, 
in cases where unusual gradings are being studied. 

3. Sampling for Preliminary Tests. Representative samples? of all 
concrete materials shall be secured for preliminary tests prior to the pro- 
portioning and mixing of the concrete. Cement test samples may be made 
up of a small quantity from each sack used in the concrete tests. Test 
samples of aggregates may be taken from larger lots by quartering. 

4. Cement Tests. Cement shall be subjected to test, using the methods 
described in the Standard Specifications and Tests for Portland Cement 
(Serial Designation: C 9) of the American Society for Testing Material.‘ 

5. Fine Aggregate Tests. Fine aggregates (passing through a No. 4 
sieve) shall be subjected, when required, to the following tests: 

(a) Sieve analysis test made in accordance with the Standard Method 
of Test for Sieve Analysis of Aggregates for Concrete (Serial Designation: 
C 41) of the American Society for Testing Materials.5 

(b) Test for organic impurities (natural sand only) made in accordance 
with the Standard Method of Test for Organic Impurities in Sands for 
Concrete (Serial Designation: C 40) of the American Society for Testing 
Materials. ® 


11924 Book of American Society for Testing Materials Standards and 
Appendix 9. 

2 For specifications for sieves, see Standard Method of Test for Sieve 
Analysis of Aggregates for Concrete (Serial Designation: C 41) of the 
American Society for Testing Materials, Appendix 3. 

3 For methods of sampling large lots of deposits of aggregate, see the 
Standard Methods of Sampling Stone, Slag, Gravel, Sand, etc., for Use as 
Highway Materials (Serial Designation: D 75) of the American Society for 
Testing Materials, 1924 Book of A. S. T. M. Standards. 

4 Appendix 1. 

5 Appendix 3. 

6 Appendix 5. 


332 CONCRETE PRACTICE 


(c) Test for quantity of silt, clay, or dust made in accordance with the 
Tentative Method of Decantation Test for Sand and Other Fine Aggre- 
gates (Serial Designation: D 136-22 T) of the American Society for Testing 
Materials. 

(d) Test for unit weight made in accordance with the Standard Method 
of Test for Unit Weight of Aggregate for Concrete (Serial Designation: 
C 29) of the American Society for Testing Materials.” 

(e) Strength test of 1:3 mortar by weight at 7 and 28 days in comparison 
with standard sand mortar. 

6. Coarse Aggregate Tests. Coarse aggregates (retained on a No. 4 
sieve) shall be subjected when required to the following tests: 

(a) Sieve analysis test as specified under Sec. 5 (a); 

(b) Test for quantity of silt, clay, or dust, as specified under See. 5 (c); 

(c) Test for unit weight as specified under Sec. 5 (d). 

7. Mixed Aggregate Tests. The unit weight of mixed fine and coarse 
aggregates as used in concrete tests shall be determined in accordance with 
the method specified in Sec. 5 (d). 

8. Proportioning. ‘The quantities of each size of aggregate to be used in 
each batch shall be determined on the basis of the sieve analysis and the 
unit weight of the mixed aggregate. The exact quantities of cement and 
of each size of aggregate for each batch shall be determined by weight. 
The quantity of water for each batch shall be accurately measured. ‘The 
quantities of materials may be expressed as (a) 1 volume of cement to — 
volumes of total aggregate mixed as used, or (b) 1 volume of cement — 
volumes fine aggregate, and — volumes of coarse aggregate. 

Notr.—It is impracticable to give a general method for proportioning 
concrete for experimental purposes; the details will necessarily vary widely 
with the purpose for which the tests are made. The following procedure 
is suggested for specific cases: 

(a) Vary the cement content by 10 per cent intervals above and below 
assumed quantity. 

(b) Vary the proportions of fine to coarse aggregate, measured sepa- 
rately, at intervals of 10 per cent. 

(c) Vary the quantity of mixing water by intervals of 10 per cent. 

9. Size of Test Pieces. Compression tests of concrete shall be made on 
cylinders of a diameter equal to one-half the length. The standard shall be 
6- X 12-in. cylinders where the coarse aggregate does not exceed 2 in. in 
size; for aggregates larger than 2 in., 8- X 16-in. cylinders shall be used; 
2- X 4-in. cylinders may be used for mixtures without coarse aggregate. 

10. Mixing Concrete. (a) Concrete shall be mixed by hand in batches 
of such size as to leave a small quantity of concrete after molding a single 
test piece. The batch shall preferably be mixed in a shallow galvanized 
steel pan with a 10-in. bricklayer’s trowel which has been blunted by cut- 
ting off about 2% in. of the point, as follows: 


1 Appendix 4. 
2 Appendix 2, 


APPENDICES 330 


(b) The cement and fine aggregate shall be mixed dry until the mixture 
is homogeneous in color; 

(c) The coarse aggregate shall be added and mixed dry; 

(d) Sufficient water shall be added to produce concrete of the required 
workability; 

Notr.—Concrete tests should be made on plastic mixtures. It is of the 
utmost importance that a uniform degree of workability be secured in tests 
involving comparisons of different materials and methods. 

(e) The whole shall be mixed thoroughly until the entire mass is homo- 
geneous in appearance. 

11. Workability. The workability or plasticity of each batch of concrete 
shall be measured immediately after mixing by one of the following methods: 

(a) Slump test made in accordance with the Tentative Method of Test 
for Consistency of Portland Cement Concrete (Serial Designation: D 138- 
25 T) of the American Society for Testing Materials.! 

(b) Flow test made by placing a metal form in the shape of a frustum 
of a cone 634 in. in top diameter, 10 in. in bottom diameter, 5 in. deep, on 
the table of the flow apparatus.2. The fresh concrete shall be placed in the 
mold in two layers. Each layer shall be puddled and finished as described 
in Sec. 18. Immediately after molding, the form shall be removed by a 
steady upward pull; the specimen raised 14 in. and dropped fifteen times 
in about 6 sec. by means of a suitable cam and crank. The spread of the 
fresh concrete due to this treatment, as compared with the original bottom 
diameter of the cone, expressed as a percentage, is the ‘‘flow.”’ 

12. Forms. The forms shall preferably be of metal. Each form shall be 
provided with a machined metal base plate, and shall be oiled with a heavy 
mineral oil before using. Particular care shall be taken to obtain tight 
forms so that the mixing water will not escape during molding. 

Notr.—The best type of form consists of lengths of cold-drawn steel 
tubing, split along one element and closed by means of a circumferential 
band and bolt. Satisfactory forms can be made from lengths of steel water- 
pipe machined on the inside, from rolled metal plates, from galvanized steel, 
machined iron or steel castings. Paraffined cardboard molds will give good 
results under expert supervision. ; 

13. Molding Test Pieces. Concrete test pieces shall be molded by placing 
the fresh concrete in the form in layers 3 to 4 in. in thickness. Each layer 
shall be puddled with twenty-five strokes with a 5g-in. round steel bar of a 
length 9 in. greater than the length of the mold, pointed at the lower end. 
After the top layer has been puddled, the surplus concrete shall be cleaned 
off with a trowel, and the mold covered with a machined metal plate or a 
piece of plate glass at least 14 in. thick, which will be used later in cap- 
ping the test piece. 


1 Appendix 7. 

2 For a description and illustration of one design for a flow table, see 
Proceedings, American Society for Testing Materials, Vol. XX, Part II, 
p. 242 (1920); and Concrete, p. 274, June, 1920. 


334 CONCRETE PRACTICE 


14. Capping Cylinders. Two to four hours after molding, the test 
pieces shall be capped with a thin layer of stiff, neat cement paste, in order 
that the cylinders may present a smooth end for loading. The cap shall be 
formed by means of a machined metal plate or a piece of plate glass of 
suitable size, at least 14 in. thick, worked down on the fresh cement paste 
until it rests on the top of the cylinder form. The cement for capping shall 
be mixed to a stiff paste before beginning to mix the concrete; in this way 
the tendency of the cap to shrink will be largely eliminated. The adhesion 
of the concrete to the metal base plate and the glass can be largely elimi- 
nated by oiling the cover plate and by inserting a sheet of paraffined tissue 
paper. 

15. Curing Test Pieces. Concrete test pieces shall be removed from 
the forms 20 to 48 hr. after molding, marked, weighed, and stored in damp 
sand, under damp cloths or in a moist chamber until the date of test. The 
temperature of the curing room should not fall outside the range of 60 to 
75°F, 

16. Age at Test. Tests shall be made at the age of 7 and 28 days; ages 
of 3 months and 1 year are recommended, if longer-time tests are required. 

17. Sequence of Tests. Three to five test pieces should be made on 
different days in investigations in which accurate comparisons are desired. 

18. Preparation of Tests. Compression tests shall be made immediately 
upon removal of the concrete test pieces from the curing room; that is, the 
test pieces shall be loaded in a damp condition. The length and average 
diameter of the test piece shall be measured in inches and hundredths; two 
diameters shall be measured at right angles near the mid-length. The 
test piece shall be weighed immediately before testing. 

19. Method of Testing. In general, only the ultimate compressive 
strength of the cylinders need be observed. The metal bearing plates of 
the testing machine shall be placed in contact with the ends of the test 
piece; cushioning materials shall not be used. An adjustable bearing block 
shall be used to transmit the load to the test piece. The bearing block 
shall be placed on top of the test piece in vertical testing machines. The 
diameter of the bearing block shall be approximately the same as that of 
the test piece. The upper section of the bearing block shall be kept in 
motion as the head of the testing machine is brought to a bearing on the 
test piece. 

20. Application of Load. The load shall be applied uniformly and with- 
out shock. The moving head of the testing machine should travel at the 
rate of about 0.05 in. per min. when the machine is running idle. 

21. Record of Tests. The total load indicated by the testing machine 
at failure of the test piece shall be recorded and the unit compressive strength 
calculated in pounds per square inch, the area computed from the average 
diameter of the cylinder being used. The type of failure and appearance 
of the concrete shall be noted. 

22. Weight of Concrete. The weight of the concrete in pounds per 
cubic foot shall be determined from the weight of the specimens and their 
dimensions, 


APPENDICES 339 


23. Density and Yield. Density and yield of concrete when required 
shall be calculated from the unit volumes of the constituent materials and 
the volume of the concrete. Density is here understood to be the ratio of 
solids in the concrete to the total volume of the mass. Yield is the volume 
of concrete resulting from one volume of aggregate mixed as used. 

24. Report of Tests. The report of tests shall include the following: 

(a) The kind and origin of concrete materials. 

(b) Complete data on all tests of cement and aggregates. 

(c) A description of methods of making and testing the concrete, where 
methods deviate from the proposed standards. 

(d) The quantities of cement, aggregates, and water in each batch. 

(e) The method of measuring workability or plasticity with ‘‘slump”’ or 
“‘flow”’ of concrete. 

(f) The quantity of water expressed as a ratio to volume of cement. 

(g) The age at test. 

(h) The size of test pieces. 

(7) The date of molding and testing each cylinder. 

(j) The compressive strength in pounds per square inch of each test 
piece and average of tests in a set. 

(k) A description of failure and appearance of concrete on each test 
piece. 

(l) The unit weight, density, and yield of the concrete. 


APPENDIX 9 


STANDARD METHODS 
OF 


MAKING AND STORING SPECIMENS OF CONCRETE IN THE 
FIELD 


American Society for Testing Materials 
Serial Designation: C 31-21 


These methods are issued under the fixed designation C 31; the final 
number indicates the year of original adoption as standard, or in the case of 
revision, the year of last revision. 


PROPOSED AS TENTATIVE, 1902; ApDoprED, 1921 


1. Scope. The methods herein specified apply to molding and storing 
of test specimens of concrete sampled from concrete being used in con- 
struction. 

2. Size and Shape of Specimen. The test specimens shall be cylindrical 
in form with the length twice the diameter. In general, a mold whose 
diameter is not less than four times the diameter of the largest size aggregate 
shall be used. (The sizes most commonly used are 6- X 12-in. and 8- X 
16-in. cylinders.) 


336 CONCRETE PRACTICE 


3. Molds. (a) The molds shall be cylindrical in form, made of non- 
absorbent material, and shall be substantial enough to hold their form 
during the molding of the test specimens. They shall not vary in diameter 
more than 14g in. in any direction, nor shall they vary in height more than 
1/¢ in. from the height required. They shall be substantially watertight, 
so that there will be no leakage of water from the test specimen during 
molding. 

(b) Each mold shall be provided with a base plate having a plane surface 
and made of non-absorbent material. This plate shall be large enough in 


; | 


ZS" ou 
+= x3 Square Head 
g =f Bolt 


| 
\3 xi Steel Pipe 


Top ‘View. 


Stock : 62'0.D. Cold- Drawn Seamless Stee! 
Tubing; 7g Walls. Make Narrow Slit along one 

Side View. Element. May also Use 6 Steel Water-Pipe, 
Machined Inside. Slit alongone Element, 
so that wher Closed will give 6" Inside 
Diameter. 


Frark 


diameter properly to support the form without leakage. Plate glass or 
planed metal is satisfactory for this purpose. A similar plate should be 
provided for covering the top surface of the test specimen after being molded. 

(c) Suggestions for suitable forms are shown in Figs. 1, 2, and 3. 

4, Sampling of Concrete. (a) Concrete for the test specimens shall be 
taken immediately after it has been placed in the work. All the concrete 
for each sample shall be taken from one place. A sufficient number of 
samples—each large enough to make one test specimen—shall be taken at 
different points so that the test specimens made from them will give a fair 
average of the concrete placed in that portion of the structure selected for 


EE EE a’ 


APPEN DICES BBv A 


tests. The location from which each sample is taken shall be noted clearly 
for future reference. 

(5) In securing samples, the concrete shall be taken from the mass by a 
shovel or similar implement and placed in a large pail or other receptacle, 
for transporting to the point of molding. Care shall be taken to see that 
each test specimen represents the total mixture of the concrete at that place. 
Different samples shall not be mixed together, but each sample shall make 
one specimen. 

5. Molding the Specimens. (a) The pails or other receptacles containing 
the samples of concrete shall be taken as quickly as possible to the place 


‘ 


TE fein eg See ey eM 


om 
wee ee mmowe oe wm Aone wwe wwe mw ew ec oon 


- 4 Sheet Iron, } ‘3x3 “Square 
kolled ene Head 
5X1 Steel Pipe Bolt 

Top View. 


k 
| 


Side View 


Fia. 2. 


selected for molding test specimens. To offset segregation of the concrete 
occurring during transportation, each sample shall be dumped into a non- 
absorbent water-tight receptacle and, after slight stirring, immediately 
placed in the mold. 

(b) The test specimens shall be molded by placing the concrete in the form 
in layers approximately 4 in. in thickness. Each layer shall be puddled 
with twenty-five to thirty strokes with a 5£- to 34-in. bar about 2 ft. long, 
tapered slightly at the lower end. After puddling the top layer, the surface 
concrete shall be struck off with a trowel and covered with the top plate, 
which will later be used in capping the test specimens. 

6. Capping Specimens. ‘Two to fourhours after molding, the test speci- 
mens shall be capped with a thin layer of stiff, neat cement paste, in order 


338 CONCRETE PRACTICE 


that the cylinder may present a smooth end for testing. The cap can best be 
formed by means of a piece of plate glass 14 in. thick, and of a diameter 2 or 3 
in. larger than that of the mold. This plate is worked on the fresh cement 
paste until it rests on top of the form. The cement for capping should 
be mixed to a stiff paste some time before it is to be used in order to avoid 
the tendency of the cap to shrink. Adhesion of the concrete to the top and 
bottom plates can be avoided by oiling the plates or by inserting a sheet of 
paraffined tissue paper. 

7. Removal of Specimens from Forms. At the end of 48 hr., the test 
specimens shall be removed from the molds and buried in damp sand, except 


Kk 
» : 
8 : 
2 8 
te 4% 
a) Ss 
8 a 
~ cy 
& _ gee 
2 Pi Pat 
3 : Lightly fae 
% ' Soldered~ or ‘Laced with Wire 
a ' Staples. 
S Top View. 
T) ' 
Ss ’ 
3 ' 
Hy ' 
A ‘ Material: 
; No. 20 Gage 
' Galvanized 
; Steel or 
Waxed Board, 
othe £02 
Side View. 
Fia. 3. 


in case the molds shown in Fig. 3 are used; in this case test specimens may 
be buried in damp sand without removal of the mold, thus permitting ship- 
ping of the test specimens in the molds. 

8. Storage of Specimens. (a) The test specimens shall remain buried in 
damp sand until 10 days prior to the date of test. They shall then be well 
packed in damp sand or wet shavings and shipped to the testing laboratory, 
where they shall be stored either in a moist room or in damp sand until the 
date of test. 

(b) Should a 7-day test be required, the test specimens shall remain at the 
works as long as possible to harden, and then shall be shipped so as to arrive 
at the laboratory in time to make the test on the required date. 


APPENDICES 339 


APPENDIX 10 


From the 1924 Report of the Joint Committee on Standard Specifications 
for Concrete and Reinforced Concrete. 


EFFECT OF OILS AND MISCELLANEOUS LIQUIDS ON CONCRETE 
AND METHOD OF PROTECTIVE TREATMENT WHERE 
REQUIRED : 


es Eff es 
Liquid seer a is Aa Surface treatment 


MINERAL Ors! 


30° Baumé or heavier. .| Good concrete unaffect- | None—Good concrete 
; ed. Very slight sur-| well spaded, or cement 


face penetration. mortar finish sufficient. 

Fuel oils above 30° || Good concrete unaffect- | Coatings of the magne- 
Baumé Distillates ed. More penetra-| sium fluosilicate class, 
Gas and lubricating tion than for heavy oils.) glues, or varnishes re- 
oils? quired for storage tanks. 


Kerosene, gasoline, | | Good concrete unaffect- | Gasoline-proof coatings 
DETID Eee fa iy cilens< ed. Considerable| producing glazed sur- 
penetration. face or treatment with 

iron compounds. 


ANIMAL O1ts (Sotip Farts)? 


Lard and lard oil....... May attack concrete| Various proprietary 
slowly, particularly if | compounds recom - 
in melted condition. mended by manufac- 

turers of technical 
paints. 

Goose fat, beef mar- | | No definite information. | Probably similar to that 

row, beef and mut- Probably similar to ; for lard oil. 
ton tallow and tal- lard oil. 
HS WGN Bayete sis Gs os 8 


1 Signal oil, used by railroads, is a mixture of animal fat with mineral oil. Probably has 
about the same effect on concrete as lard oils. 

2 Some lubricating oils are mixtures of mineral and animal oils. 

3 Bureau of Standards tests with concrete tanks show slight roughening of surface at end of 
12 months, and considerable deposit on surface through saponification. 


340 CONCRETE PRACTICE 


Liquid ect on untreated Surface treatment 
concrete 


ANIMAL O1Ls (Liguip Farts) 


Marine: 
Menhaden oil........ No effect on good con- | Cushman’s tests indicate 
crete. various coatings no bet- 
ter than plain concrete. 
Cod liver GiLe .; 42 More or less disintegra- | Various proprietary 
Shark liver oil..... tion depending on qual-| compounds recom- 
Seal and whale oil.. ity of concrete. mended by manufac- 
turers of technical 
paints. 
Terrestrial: ) 
Sheep’s foot...... | More or less disintegra- | Various proprietary 
Horse’s foot...... tion depending on qual-| compounds recom - 
ity of concrete. mended by manufac- 
turers of technical 
paints. 
Neat a:f0ot*=. asa. No effect on good con-| No treatment required. 


crete. 
VEGETABLE O1Ls (Souip Fats) 


Cocostut Gis eio7. nee Some action if stored in | Several proprietary com- 
closed tank. Progres-| pounds seem to have 
sive disintegration ifin| proved effective on 
contact with surfaces| floors. Sodium silicate 
exposed to air. or magnesium fluosili- 

cate treatment appar- 
ently sufficient for 
closed tanks. 


Palm oilt¢s 2 eee No information. No information. 
VEGETABLE OILS 
Drying: 


Poppyseed oil..... No information. No information. 


1 Bureau of Standards noted slight deposit due to saponification at end of 12 months. 
2 Bureau of Standards tests with concrete tanks show considerable softening and roughen- 
ing of surface at end of 12 months, 


APPENDICES 


341 


Effect on untreated 


ao concrete 


Surface treatment 


VEGETABLE Oris (Continued) 


Linseed oil!........ No effect on good con- 


Hosmtolpes. kt... crete. Considerable 
Turpentine........ penetration of turpen- 
tine. 
Semidrying: 


No action if stored in 
closed tank of good con- 
crete. 


Cottonseed oil....... 


Progressive disintegra- 
tion, if in contact with 
surfaces exposed to air. 


Rape seed oil...... 
PaStOrOll... 2... . 
Mustard oil....... 


Non-drying: 


Eh Ce Probably some action. 


Butter oil (2) 


MIscELLANEOUS LIQUIDS 


Cushman’s tests indicate 
various coatings no bet- 
ter than plain concrete 
for linseed and rosin 
oils. 


Same as for cocoanut oil. 


Cushman’s tests show 
proprietary coatings of 
varnish type effective. 


Tanning liquors........ 
siderable effect. Other 
tanning extracts have 
no action. 


Attacks untreated con- 
crete tanks. 


Snlnte uguor.: i. +... .. 


Acetic acid attacks con- 
crete. 


Cider vinegar. .../..... 


Acid liquors show con-| Bituminous acid-proof 


paints effective for 
tanks holding acid tan- 
ning solutions. Good 
concrete with or with- 
out mortar finish suffi- 
cient for other tanning 
liquors. 


Cushman’s tests indicate 

bituminous acid-proof 
paints effective. Par- 
affin coating fair. 


Cushman’s tests indicate 

bituminous acid-proof 
paints effective. Par- 
affin coatings applied 
hot also useful for 
tanks. 


1 Bureau of Standards noted at end of 12 months considerable deposit on surfaces of 
concrete tanks containing both boiled and raw linseed oil, due to saponification, but concrete 


showed no deterioration. 


342 CONCRETE PRACTICE 


Tawaid Effect on untreated 


Surface treatment 
concrete 


‘MisceLLANEous Liquips (Continued) 


Sauerkraut brine....... No action on good con-| Cushman’s tests show 
crete. special treatments no 
better than untreated 

concrete. 
W hey.i tien es eres More or less action de-| Cushman’s tests show 
pending on quality of| proprietary coating of 
concrete. varnish type effective. 


Sodium silicate treat- 
ment used on storage 


tanks. 
Buttermilk. oan. 1.7 eae No action on good con-| Untreated tanks used 
crete. successfully to store 
buttermilk. 
Molasses..............]| No action in closed con- | Good concrete well spad- 
crete. ed or finished with 


cement mortar  suffi- 
cient. Annapolis mix- 
ture sometimes used. 


Sulfuric acid solutions. .| Progressive disintegra-| Bituminous  acid-proof 
tion, particularly where] paints or mastic coat- 
concrete is subject to| ing effective. 
abrasion. 


APPENDIX 11 


STANDARD SPECIFICATIONS FOR CONCRETE BUILDING BLOCK 
AND CONCRETE BUILDING TILE 


American Concrete Institute 
Submitted by Committee P-1, on Standard Building Units 
Serial Designation P—1A—25 


1. GENERAL 


1. The purpose of these specifications is to define the requirements for 
concrete building block and concrete building tile to be used in construction. 

2. The word ‘‘concrete”’ shall be understood to mean portland cement 
concrete. 


I 


APPENDICES 343 


3. Strength Requirements. According to the strength in compression 
28 days after being manufactured or when shipped, concrete block and 
concrete tile shall be classified as heavy-load-bearing, load-bearing, and 
non-load-bearing on the basis of the following requirements: 


Compressive strength, pounds per 
square inch of gross cross-sectional 


Name of classification area as laid in the wall 


Minimum for in- 
dividual unit 


Average of 3 or 
more units 


Heavy-load-bearing block or tile.......... 1200 1000 
Medium-load-bearing block or tile........ 700 600 


Non-load-bearing block or tile........... 7 250 | 200 


4. The gross cross-sectional area of a one-piece concrete block or tile shall 
be considered as the product of the length times the width of the unit as laid 
in the wall. No allowance shall be made for air spaces in hollow units. 
The gross cross-sectional area of each unit of a two-piece block or tile shall 
be considered the product of the length of the unit times one-half the thick-' 
ness of the wall for which the two-piece block or tile is intended. 

5. The compressive strength of the concrete in units of all classifications 
except “‘non-load-bearing block” shall be at least 1000 lb. per sq. in., when 
calculated on the minimum cross-sectional area in bearing. 

6. Absorption Requirements. Concrete building block and tile to be 
exposed to soil or weather in the finished work (without stucco, plaster, or 
other suitable protective covering) shall meet the requirements of the absorp- 
tion test. 

7. All concrete building block and tile not covered by Paragraph 6 need 
not meet an absorption requirement. 

8. Concrete block and tile shall not absorb more than 10 per cent of the 
dry weight of the unit, when tested as hereinafter specified, except when it 
is made of concrete weighing less than 140 lb. per cu. ft. For block or tile 
made with concrete weighing less than 140 lb. per cu. ft., the absorption in 
per cent by weight shall not be more than 10 multiplied by 140 and 
divided by the unit weight in pounds per cubic foot of the concrete under 
consideration. 

9. Sampling.—Specimens for tests shall be representative of the com- 
mercial product of the plant. 

10. Not less than three and preferably five specimens shall be required 
for each test. 

11. The specimens used in the absorption test may be used for the 
strength test. 


2. METHODS OF TESTING 
12. Absorption Test.—The specimens shall be immersed in clean water at 


approximately 70°F. for a period of 24 hr. They shall then be removed, 
the surface water wiped off, and the specimens weighed. Specimens shall 


344 CONCRETE PRACTICE 


be dried to a constant weight at a temperature of from 212 to 250°F. and 
reweighed. Absorption is the difference in weight divided by the weight 
of the dry specimens and multiplied by 100. 

13. Weight of Concrete.—The weight per cubic foot of the concrete in a 
block or tile is the weight of the unit in pounds divided by its volume in 
cubic feet. To obtain the volume of the unit, fill a vessel with enough water 
to immerse the specimen. The greatest accuracy will be obtained with the 
smallest vessel in which the specimen can be immersed with its length 
vertical. Mark the level of the water, then immerse the saturated specimen 
and weigh the vessel. Draw the water down to its original level, and weigh 
the vessel again. The difference between the two weights divided by 62.5 
equals the volume of the specimen in cubic feet. 

14. Strength Test.—Specimens for the strength test shall be dried to 
constant weight at a temperature of from 212 to 250°F. 

15. The specimens to be tested shall be carefully measured for overall 
dimensions of length, width, and height. 

16. Bearing surfaces shall be made plane by capping with plaster of paris 
or a mixture of portland cement and plaster, which shall be allowed to 
harden thoroughly before the test. 

17. Specimens shall be accurately centered in the testing machine. | 

18. The load shall be applied through a spherical bearing block placed on 
top of the specimen. 

19. When testing other than rectangular block or tile, care must be 
taken to see that the load is applied through the center of gravity of the 
specimen. 

20. Metal plates of sufficient thickness to prevent appreciable bending 
shall be placed between the spherical bearing block and the specimen. 

21. The specimen shall be loaded to failure. 

22. The compressive strength in pounds per square inch of gross cross- 
sectional area is the total applied load in pounds divided by the gross cross- 
sectional area in square inches. 


APPENDIX 12 


STANDARD SPECIFICATION FOR CONCRETE BRICK 
Submitted by Committee P-1, on Standard Building Units 
American Concrete Institute 
(Serial Designation P-1B-25) 


1. GENERAL 


1. The purpose of these specifications is to define the requirements for 
concrete brick to be used in construction. 


APPENDICES 345 


2. The word “concrete” shall be understood to mean portland cement 
concrete. 

3. The average compressive strength of concrete brick 28 days after 
being manufactured or when shipped shall not be less than 1500 lb. per sq. 
in. of gross cross-sectional area as laid in the wall, and the compressive 
strength of any individual brick shall be not less than 1000 lb. per sq. in. 
of gross cross-sectional area as laid in the wall. 

4. The gross cross-sectional area of a brick shall be considered as the 
product of the length times the width of the unit as laid in the wall. 

5. Concrete brick shall not absorb more than 12 per cent of the dry 
weight of the brick when tested as hereinafter specified, except when they 
are made of concrete weighing less than 125 lb. per cu. ft. For brick made 
of concrete weighing less than 125 lb. per cu. ft., the average absorption 
in per cent by weight shall not be more than 12 multiplied by 125 and 
divided by the unit weight in pounds per cubic foot of the concrete under 
consideration. 

6. Specimens for tests shall be representative of the commercial product 
of the plant. 

7. Five specimens shall be required for each test. 

8. The specimens used in the absorption test may be used for the strength 
test. 


2. METHODS OF TESTING 


9. Absorption Test.—The specimens shall be immersed in clean water 
at approximately 70°F. for a period of 24 hr. They shall then be removed, 
the surface water wiped off, and the specimens weighed. Specimens shall 
be dried to a constant weight at a temperature of from 212 to 250°F., and 
reweighed. Absorption is the difference in weight divided by the weight of 
the dry specimens and multiplied by 100. 

10. Strength Test.—Specimens for the strength test shall be dried to 
constant weight at a temperature of from 212 to 250°F. 

11. The specimens to be tested shall be carefully measured for overall 
dimensions of length, width, and thickness. 

12. Bearing surfaces shall be made plane by capping with plaster of 
Paris or a mixture of portland cement and plaster, which shall be allowed to 
harden thoroughly before the test. 

13. Specimens shall be accurately centered in the testing machine. 

14. The load shall be applied through a spherical bearing block placed 
on top of the specimen. 

15. Metal plates of sufficient thickness to prevent appreciable bending 
shall be placed between the spherical bearing block and the specimen. 

16. The specimen shall be loaded to failure. 

17. The compressive strength in pounds per square inch of gross cross- 
sectional area is the total applied load in pounds divided by gross cross- 
sectional area in square inches, 


346 CONCRETE PRACTICE 


APPENDIX 13 


SPECIFICATIONS FOR 
PORTLAND CEMENT CONCRETE PAVEMENTS 


American Concrete Institute 


ONE-COURSE PORTLAND CEMENT CONCRETE 
PAVEMENTS FOR HIGHWAYS 


I. GENERAL 


1. It is the intent of these specifications to cover the requirements for 
the materials and construction of Portland Cement Concrete Highway 
Pavement wherein the concrete is of uniform proportions from top to bot- 
tom of slab. 


II. MATERIALS 


(A) Cement 


2. Cement shall be a standard portland cement which, at the time it is 
incorporated in the pavement mixture, shall conform to the Standard 
Specifications and Tests for Portland Cement (Serial Designation: C 9-21) 
of the American Society for Testing Materials, and subsequent revisions 
thereof, 


(B) Aggregates 


3. Prior to placing any orders for aggregates, the contractor shall advise 
the engineer of the proposed source or sources of supply of aggregates. 
The engineer may require the contractor to submit 50-lb. samples of all 
aggregates proposed for use. If the engineer finds such samples fulfill 
the requirements of these specifications for aggregates, similar material 
shall be considered as acceptable. Acceptance of samples shall not be 
construed as a guarantee of acceptance of all materials from the same source, 
and it shall be understood that any aggregates which do not meet with the 
requirements of these specifications will be rejected. Upon receiving noti- 
fication of the proposed source or sources of aggregate supply, the engineer 
may elect to investigate and test the aggregate supply at the source; in 
which case he shall notify the contractor as to acceptability, or non-accept- 
ability of the proposed aggregates. ‘The engineer shall notify the con- 
tractor, after agreement upon a source or sources of aggregate supply, 
whether routine tests of aggregates during construction will be made at the 
source of supply or at the point of receipt. 

4. (a) Fine Aggregate.—Fine aggregate shall consist of natural sand, 
stone screenings, slag sand, tailings, chatts, or other inert materials with 


APPENDICES 047 


similar characteristics, or a combination thereof, having clean, hard, strong, 
durable, uncoated grains. When incorporated in the pavement mixture, 
fine aggregate shall be free from frost, frozen lumps, injurious amounts of 
dust, mica, soft or flaky particles, shale, alkali, organic matter, loam, or 
other deleterious substances. Ninety-five per cent of the fine aggregate, 
when dry, shall pass a one-fourth (14)-inch sieve; not more than 25 per cent 
shall pass a 50-mesh sieve, and not more than 5 per cent by weight shall 
pass a 100-mesh sieve. In no case shall fine aggregate be accepted con- 
taining more than 3 per cent, by dry weight, nor more than 5 per cent by 
dry volume, nor more than 7 per cent by wet volume, of clay, loam, or silt. 
If any sample of fine aggregate shows more than 7 per cent of clay, loam, 
or silt, in 1 hr.’s settlement after shaking in an excess of water, the material 
represented by the sample will be rejected. Fine aggregate shall be of 
such a quality that mortar composed of portland cement and the fine 
aggregate, when made into 2- X 4-in. cylinders, in the same proportions 
as will be used in the concrete mixture for the pavement, shall show com- 
pressive strength at 7 and 28 days equal to, or greater than, the compressive 
strength of cylinders composed of mortar of the same proportions of port- 
land cement and standard Ottawa sand. For proportioning test cylinders, 
portland cement and fine aggregate and standard Ottawa sand shall be 
measured by weight and the same portland cement shall be used with the 
Ottawa sand as with the fine aggregate to be tested. 

5. (b) Coarse Aggregate.-—Coarse aggregate shall consist of one of the 
following materials, or a combination thereof; crushed rock, pebbles (gravel), 
air-cooled blast-furnace slag, chatts, or tailings. The particles of coarse 
aggregate shall be of clean, hard, tough, durable material, free from vege- 
table or other deleterious substances, and shall contain no soft, flat, or 
elongated pieces. Coarse aggregate, except air-cooled blast-furnace slag, 
shall show not more than 6 per cent loss in the wear test. 

(Nore: In many cases, it will be necessary for the engineer to specify the 
sizes, grading, and quality of coarse aggregate in accordance with local 
conditions. In every case, the engineer should provide specifications which 
will require the use of the best coarse aggregate which is economically 
available. The following specifications covering size and grading of coarse 
aggregate will be found applicable in most sections of the country, and 
are intended for use with the 1:2:3%, 1:2:3, or 1:114:3, mixture.) 

6. The size of the coarse aggregate shall be such as to pass a 3-in. round 
opening. Coarse aggregate shall be uniformly graded within the limits 
shown in the following table, and any material which does not come within 
the limits specified shall be rejected. 

Passing 3-in. round opening, 100 per cent. 

Passing 2-in. round opening, not less than 82 per cent nor more than 95 
per cent. 

Passing 4-in. round opening, not less than 15 per cent nor more than 
25 per cent. 

Passing 14-in. sieve, not more than 5 per cent. 


348 CONCRETE PRACTICE 


7. Crushed rock shall consist of particles of rock produced by quarrying 
and crushing ledge rock, field boulders, or pebbles, from which, after crush- 
ing, all dust and pieces below one-quarter (14)-inch size have been screened 
out. Crushed rock shall conform in quality to the specifications under 
‘“‘Coarse Aggregate.” 

8. Pebbles (gravel) shall consist of loose material containing only particles 
retained upon a 14-in. sieve, resulting from the natural crushing and ero- 
sion of rocks. Pebbles must have wearing qualities at least equal to crushed 
stone. Pebbles shall conform in quality to the specifications under ‘‘ Coarse 
Aggregate.” 

9. Air-cooled blast-furnace slag—The broken slag shall consist of roughly 
cubical fragments of air-cooled blast-furnace slag, reasonably uniform in 
density and quality and reasonably free from metallic iron, containing no 
dirt or other objectionable matter. The slag shall weigh not less than 
seventy (70) pound per cu. ft. 

10. Chatts, or tailings, are terms locally applied to by-products, or waste 
products, of certain mining and industrial operations. When used as 
coarse aggregate for concrete pavements, such materials shall substantially 
conform to the specifications under ‘‘Coarse Aggregate.” 

11. (c) Mixed Aggregate-—Mixed aggregate shall consist of a combina- 
tion of fine and coarse aggregates. That portion of mixed aggregate passing 
a one-quarter (14)-inch sieve shall conform to the requirements for fine 
aggregate; and that portion of mixed aggregate retained on a one-quarter 
(14)-inch sieve shall conform to the requirements for coarse aggregate. 


(C) Water 
12. Water shall be clean, free from oil, acid, alkali, or vegetable matter. 
(D) Reinforcement 


13. Reinforcement shall consist of steel fabric, or of steel bars, or a com- 
bination of both, and shall have an effective weight exclusive of dowel bars 
at joints and of circumferential bars of at least ...... lb. per 100 sq. ft. 

14. (a) Steel Fabric.—Steel fabric shall be manufactured from cold- 
drawn wire, and shall comply with tentative standards of the American 
Society for Testing Materials, Serial Designation A 82-21 T. 

15. The spacing of primary members shall be not more than ...... in., 
and of secondary members not more than ...... in. 

16. (b) Steel Bar Reinforcement.—This style of reinforcement shall 
consist of steel bars of the size, shape, and spacing shown on the plans, and 
shall be properly formed into mats. All intersections of longitudinal 
and transverse bars along the exterior edges of the mat and every other 
intersection of the longitudinal and transverse bars in the interior of the 
mat shall be securely wired or clipped together to resist displacement 
during handling and concreting operations. ‘The materials shall have an 
effective weight of not less than ...... lb. per 100 sq. ft., exclusive of laps, 
ties, clamps, chairs, and such portions of the bars as are not in the plane of 
the mat for their full lengths. 


APPENDICES 349 


17. Steel bars shall comply with the standard requirements for concrete 
reinforcement bars, structural and intermediate grades, of the American 
Society for Testing Materials, Serial Designation A 15-14. All bar rein- 
forcement, when placed in the pavement, shall be free from excess rust, 
scale or other substance which prevents the bonding of the concrete to 
the reinforcement. When in storage on the work, bars shall be protected 
from corrosion by placing them on a dry platform under a weatherproof 
cover. 


(E) Joint Filler 


18. Joint filler shall consist of prepared strips of fiber matrix and bitu- 
men, containing not more than 25 per cent of inert material, having 
thickness of ...... in., and width equal to ...... in. greater than the 


_ thickness of the pavement at any point. The bitumen used in manufacture 


of the joint filler may be either tar or asphalt of a grade that will not 
become soft enough to flow in hot weather, nor brittle in cold weather. 
The prepared strips shall be cut to conform to the cross-section of the pave- 
ment and in lengths equal to the width of the pavement, except that strips 
equal in length to half the width of the pavement may be used when laced 
or clipped together at the center in a workmanlike and effective manner. 


(F) Shoulders 


19. (Any special materials for the construction of shoulders should be 
here described as desired by the engineer.) 


lil. SUBGRADE 


20. Subgrade will be considered as that portion of the highway upon 
which the pavement is to be placed. 


(A) Fine Grading 


21. Fine grading will include the finished excavation and embankment 
which may be necessary to bring the subgrade to the required elevation, 
alignment, and cross-section. All suitable materials removed from the 
excavation in fine grading shall be used as far as practicable in the forma- 
tion of the embankment, as may be required. Such material not used in 
embankment may be deposited on the shoulders as directed by the engi- 
neer. When the amount of the embankment exceeds the amount -of the 
material available from excavation, suitable material shall be obtained by 
the contractor from borrow pits located beyond the limits of the shoulders 
or embankment slopes. Such borrow pits shall be left in neat condition, 
such as will drain completely. Ditch sections and back slopes of cuts 
must conform to the plans, and be left with neat and uniform appearance. 


(B) Preparation and Maintenance 


22. The subgrade shall be constructed to have, as nearly as practicable, 
a uniform density throughout its entire width. Wherever the subgrade 


350 CONCRETE PRACTICE 


extends beyond the lateral limits of an old roadway, or wherever an old 
gravel, macadam, or other hard, compared crust comes within 6 in. of the 
elevation of the finished subgrade, such old roadway or crust shall be 
ploughed, loosened, or scarified to a depth of at least 6 in., and the loosened 
material redistributed across the full width of the subgrade, adding suit- 
able material, when necessary, so that when compacted to the required 
elevation, alignment, and cross-section, the subgrade will approach, as 
nearly as possible, a condition of uniform density. Compression of the 
subgrade material shall be accomplished with a self-propelled roller weigh- 
ing not less than 3 tons. Hand-tamping portions of the subgrade may be 
directed by the engineer when necessary, ‘There shall not be left on the 
subgrade or shoulders, berms or ridges of earth or other material that 
will interfere with the immediate discharge of water from the subgrade 
to the side ditches, and the subgrade shall be maintained free from ruts 
so that it will, at all times, drain properly. 

23. All depressions developing under traffic on the subgrade, or in con- 
nection with rolling, shall be filled with suitable material. Rolling shall 
be continued until the subgrade is uniformly compacted, properly shaped, 
and true to grade and alignment. It is not intended that the rolling shall 
be continued beyond this point, as the purpose of rolling is not to produce 
a subgrade that cannot be further compacted, but to produce a uniformly 
compacted subgrade. All hauling shall be distributed over the width of 
the subgrade so far as practicable, so as to leave it in a uniformly compacted 
condition. 

24. After being prepared in the above manner, the subgrade shall be so 
maintained until the concrete pavement has been placed thereon. 


(C) Checking and Acceptance 


25. Immediately prior to placing concrete pavement on the subgrade, 
it shall be checked by means of an approved scratch template, resting on 
the side forms, having the scratch points placed not less than 8 in. apart, 
and to the exact elevation and cross-section for the subgrade surface. The 
scratch template shall be drawn along the forms so that the plane of the 
points will be at a right angle to the grade line, and the long axis of 
the template at a right angle to the center line of the pavement. All high 
places indicated by the scratch points shall be removed to trude grade, and 
any low places back filled with suitable material, and rolled or hand-tamped 
until smooth and firm. The subgrade shall be checked and completed in 
accordance with these requirements for a distance of not less than 100 ft. 
in advance of the concrete. If hauling over the subgrade after it has been 
finished and checked as above specified results in ruts or other objection- 
able irregularities, the contractor shall reroll or hand-tamp the subgrade 
and place it in smooth and satisfactory condition before the pavement is 
deposited upon it. If the condition of the subgrade is such that it can- 
not be placed in satisfactory condition to receive the pavement by the 
above methods, placing pavement may be stopped by the engineer, unless 
the contractor can provide and haul over suitable trackways or use other 
satisfactory means for the protection and maintenance of the subgrade. 


APPENDICES dol 


(D) Special Treatment 


26. (Special treatment may be specified for certain subgrades such as sand, 
gumbo, adobe, and other materials, which cannot be satisfactorily prepared 
for pavement by the methods specified in the foregoing paragraphs.) 


IV. FORMS 


(A) Materials 


27. Wooden forms shall be dressed to 3-in. thickness, and equal in depth 
to the thickness of the pavement at the sides. Forms shall rest upon stakes 
driven into the ground within 1 ft. of each end of each separate piece, and at 
intervals not greater than 5 ft. elsewhere. Forms shall be held by stakes 
. driven into the ground along the outside edge at intervals of not more than 
6 ft., two stakes being placed at each joint. The forms shall be firmly nailed 
to the side stakes, and firmly braced at any point where necessary to resist 
the pressure of the concrete or the impact of the tamper. Forms shall be 
capped along the inside upper edge with 2-in. angle irons. 

28. Metal forms shall be of shaped steel sections not less than 10 ft. in 
length, for tangents and for curves having radii of 150 ft. and over. For 
curves of less radii, sections 5 ft. long may be used. Forms must have a 
depth equal to the side thickness of the pavement. Forms shall be made of 
steel plate of approved section. At least three bracing pins or stakes shall 
be used to each 10 ft. of form, and the bracing and support must be ample 
to resist the pressure of the concrete and the impact of the tamper without 
springing. 

(B) Setting 

29. Forms shall be set to exact grade and alignment at least 500 ft. in 
advance of the point of depositing concrete. Before setting, the sections 
must be thoroughly cleaned. After setting, they shall be thoroughly oiled 
before concrete is placed against them. Forms in place will be subject to 
check and correlation of line or grade at any time. 


V. PAVEMENT SECTION 


30. Width, thickness, and crown of concrete pavement shall be as shown 
on the plans for the improvement. 


VI. JOINTS 


31. The joints to be formed shall be transverse or longitudinal. They 
shall be tested during and after finishing with a 10-ft. straightedge, and any 
irregularities in the surface shall be immediately corrected. Expansion 
joints shall be formed between the pavement under construction, and all 
other rigid types of pavement or structures to whichit may be adjacent. All 
joints shall be edged to a radius of } in. Joints shall be made as follows: 


(A) Transverse Expansion Joints 


32. Transverse expansion joints shall be .......... in. wide, spaced 
eeranhir ss ft. apart. A bulkhead cut to the exact cross-section of the 


302 CONCRETE PRACTICE 


pavement shall be securely staked in place at right angles to the center 
line and surface of the pavement. The premolded joint filler shall be placed 
against the bulkhead and held in position by pins on which there is an 
outstanding lug. Concrete shall be deposited on both sides of the bulkhead 
before it is removed. After the concrete has been struck off, the bulkhead 
shall be removed by lifting it slowly from one end and replacing it with 
concrete as it is lifted, so that the joint filler will be left in the correct position. 

33. When expansion joints are made at the end of the day’s work, they 
shall be formed by finishing the concrete to the bulkhead, placed as before 
specified. When work is resumed, the joint filler shall be placed against the 
hardened concrete, and held in position by pins until fresh concrete is placed 
against it. 

34. In pavements with integral curb, the joint shall be continuous in a 
straight line through pavement and curb. 

35. Joints shall be opened on the edges for their entire depth, upon 
removal of the forms. 

36. Before the pavement is ges to traffic the joint filler shall be 
trimmed off to a uniform height of }4 in. above the surface of the pavement. 


(B) Longitudinal Expansion Joints 


37. Longitudinal expansion joints shall be formed by placing the filler 
against the form, bulkhead, curb, or adjacent structure and placing the 
concrete against it. The filler shall extend the full depth of the pavement, 
and be flush with the pavement surface. 


(C) Transverse Construction Joints 


38. Transverse construction joints shall be formed whenever it is necessary 
to stop concreting for 30 min. or longer, except at expansion joints, by stak- 
ing in place a bulkhead, as specified for transverse expansion joints, and 
finishing the concrete to the bulkhead. An edging tool shall be used along 
the bulkhead to make the construction joint a regular and well-defined line. 
When the plans require steel dowels across transverse joints in this bulkhead 
there shall be holes spaced 3 ft., center to center, 3 in. below the surface of the 
finished pavement, through which 34-in. plain round steel rods 4 ft. long shall 
be inserted with 2 ft. projecting. At least one-half length of each bar shall 
be encased in heavy paper or coated with paint or oil in such a manner as to 
prevent a bond between the steel and the concrete. 

39. When work is resumed, the plank shall be removed, care cane taken 
not to disturb the rods or the concrete. The fresh concrete shall be placed: 
directly against the face of the concrete previously laid and carefully worked 
around the rods. 

40. If concreting must be stopped within 10 ft. of a previously made trans- 
verse joint, the concrete shall be removed to this joint. 


(D) Longitudinal Construction Joints 


41. Longitudinal construction joints shall be formed where required, and 
must be straight and vertical. When so indicated on the plans, steel dowles 
shall be used as provided in the preceding section. 


APPENDICES 300 


VII. WATER SUPPLY 


(A) Equipment 

42. Where necessary for the supply of water for all operations described 
in these specifications, duplicate pumps, connected to an adequate pipe line 
along the improvement, shall be provided by the contractor. The pipe line 
must be fitted with drains at the low points, and air relief valves at the high 
points, and with convenient outlets for all paving operations. Where the 
concrete mixer operates on the subgrade, the pipe line shall have a minimum 
diameter of 2in. For supplying a mixer using more than 4 sacks of cement 
per batch, 60 per cent of the pipe line shall have a minimum diameter 
of 3 in., and the remaining 40 per cent shall have a minimum diameter of 
2in. The large diameter pipe shall lead from the pump. 


(B) Priority to Water Supply 


43. The concrete pavement in place, for 10 days after laying, and the 
subgrade preparation, shall have prior rights to the water supply. If it 
should develop there is not sufficient water for all purposes, the concrete 
mixer shall be shut down until the water needs of the curing and subgrading 
operations have been cared for. 


VIII. PROPORTIONING AND MIXING CONCRETE 
(A) Proportioning 


44, (a) Measuring Materials.—The method of measuring materials for the 
concrete, including water, shall be such as to insure the required proportions 
of each of the materials as directed by these specifications. One sack of 
portland cement (94 lb. net) shall be considered 1 cu. ft. 

45. (b) Proportions.—The concrete shall be proportioned 1 sack of port- 
land cement, not more than ............ cu. ft. of fine aggregate, and not 
MOPS AGM Pe cu. ft. of coarse aggregate. A cu. yd. of concrete 
in place, measured between neat lines, must contain ............ barrels 
of portland cement. ‘The engineer shall compare the calculated amount of 
cement required by these specifications with the amounts actually used in 
@ach. section Of concrete ............ ft. long, or between successive 
transverse joints. If the amount of cement actually used in the pavement 
varies from the specified amount by more than 3 per cent for any section, the 
engineer may require the proportions of the concrete to be adjusted so as to 
use the specified amount of cement. If it is found that the amount of cement 
used in any section is 9214 per cent, or less, of the specified quantity, the 
contractor shall be required to remove such section or sections, and replace 
them with concrete made in accordance with these specifications. Such 
removal and replacement shall be done at the expense of the contractor. 


(B) Mixing 
46. (a) Operation of Mixer.—The concrete shall be mixed in a batch mixer, 
with the “boom and bucket” type of delivery. The capacity of the drum 


354 CONCRETE PRACTICE 


shall be such that only whole bags of cement are used in each batch. Mix- 
ing shall continue for at least 1 min. after all materials, including water, are 
placed in the drum, and before any part of the batch is discharged. The 
drum shall be revolved not less than 14 nor more than 18 revolutions per 
minute. The drum shali be completely emptied before receiving materials 
for the succeeding batch. ‘The volume of the mixed material in each batch 
shall not exceed the mixer manufacturer’s rated capacity of the drum. 

47. The mixer shall be provided with a water measuring tank into which 
mixing water shall be discharged, having a visible gage so that the amount 
of water for each batch may be separately and accurately measured. The 
mixer shall be provided with an approved batch-timing device, which will 
automatically lock the batch-discharging device during the full mixing time 
and release it at the end of the mixing period. The timer device shall have a 
bell which will automatically ring at the end of the mixing period. This 
device shall be subject to inspection and adjustment by the engineer at any 
time. 

48. (b) Retempering.—Mortar or concrete which has partially set shall 
not be retempered by being mixed with additional materials or water. 

49. (c) Central Mixing Plants.—The use of central mixing plants and the 
transportation of mixed concrete is permitted under these specifications, 
provided there is no segregation of the mixed concrete, when it is delivered 
at the point where it is to be deposited in the pavement. ‘The period between 
mixing and placing in the pavement shall not exceed 40 min., and this period 
may be reduced at the direction of the engineer. The concrete must be of 
workable consistency when placed on the subgrade. ~ Be 

50. (d) Consistency.—The concrete mixture shall contain no more water 


than is necessary to produce a workable mass which can be brought to a 


satisfactory finish in the pavement. The amount of water used shall not 
exceed 614 gal. per sack of cement, when the aggregates are dry. 


IX. PLACING CONCRETE AND REINFORCEMENT 
(A) Inspection of Subgrade 


51. (a) Rechecking Subgrade.—Immediately before placing concrete, or 
any type of reinforcement, the subgrade shall be rechecked by means of a 
scratch template as provided in paragraph 25 of these specifications, and 
any inequalities corrected as therein provided. 

52. (b) Condition of Subgrade.—Concrete shall be placed only on a moist 
subgrade, but there shall be no pools of standing water. If the subgrade 
is dry, it shall be sprinkled with as much water as it will absorb readily, 
The engineer may direct that the subgrade be sprinkled or thoroughly wet 
down from 12 to 36 hr. in advance of placing concrete, where such procedure 
may be deemed necessary. 


(B) Placing Reinforcement 


53. Steel fabric reinforcement of the size and weight shown on the plans 
shall be placed 2 in. below and parallel to the finished surface of the pavement 


- ~~) ae 


APPENDICES 355 


unless otherwise indicated. Fabric shall extend to within 2 in. of sides 
and ends of slabs. All laps of fabric sections shall be not less than three- 
fourths of the spacing of members in the direction lapped. Steel bar 
reinforcement shall be placed 3 in. below the finished surface of the pave- 
ment unless otherwise indicated on the plans. Transverse bars shall extend 
to within 2 in. of the margins of the pavement. Bar reinforcement shall be 
placed and securely supported in correct position before any concrete is laid. 
All intersections of longitudinal and transverse bars shall be securely wired 
or clipped together to resist displacement during concreting operations. 


(C) Placing Concrete 


54. The mixed concrete shall be deposited rapidly on the subgrade to the 
required depth and for the entire width of the pavement section, in successive 
batches and in a continuous operation without the use of intermediate forms 
or bulkheads between joints. While being placed, the concrete shall be 
vigorously sliced and spaded with suitable tools to prevent formation of voids 
or honeycomb pockets. ‘The concrete shall be especially well spaded and 
tamped against the forms. When the concrete is placed in two horizontal 
layers to permit use of steel reinforcement, the first layer shall be roughly 
struck off with a template or screed, riding on the side forms, at the correct 
elevation to permit placing the reinforcement in specified position. The 
concrete above the reinforcement shall be placed within 15 min. after the 
first layer has been placed. Any dust, dirt, or foreign matter which collects 
on the first layer shall be carefully removed before the upper layer is placed. 

55. Whenever the placing of concrete is to be suspended for more than 30 
min., a transverse joint shall be formed, at the point directed by the engineer 
to close the section. Any concrete in excess of that needed to complete a 
section, when work is stopped for more than 30 min., shall not be used in the 
pavement. 


(D) Finishing 


56. (a) General.—Experienced and skilful workmen must be employed 
at all times for preparing the surface of the pavement. The concrete shall 
be brought to the specified contour by means of a heavy screed or template, 
fitted with handles, weighing not less than 15 lb. per lin. ft. This screed or 
template may be of steel, or of wood shod with steel. It shall be shaped to 
the cross-section of the pavement, and have sufficient strength to retain its 
shape under all working conditions. The template or screed shall rest on the 
side forms and shall be drawn ahead with a sawing motion. At transverse 
joints, the template shall be drawn not closer than 3 ft. toward the joint, and 
shall then be lifted and set down at the joint and drawn backwards away 
therefrom. Surplus concrete shall then be taken up with shovels and 
thrown ahead of the joint. 

57. (b) Belting.—The concrete shall be finished by using a belt of wood, 
canvas, or rubber, not less than 6 nor more than 12 in. wide, and at least 
2 ft. longer than the width of the pavement. The belt shall be applied 
with a combined crosswise and longitudinal motion. For the first applica- 


356 CONCRETE PRACTICE 


tion, vigorous strokes at least 12 in. long shall be used, and the longitudinal 
movement along the pavement shall be very slight. The second applica- 
tion of the belt shall be immediately after the water sheen disappears, and 
the stroke of the belt shall be not more than 4 in. and the longitudinal 
movement shall be greater than for the first belting. 

58. (c) Machine Finishing.—When a finishing machine is used, it shall 
be so designed and operated as to strike off and consolidate the concrete, 
eliminating ridges and producing a true and even surface. The operation 
of the machine shall be so controlled as to keep the coarse aggregate near 
the finished surface of the pavement. Repeated operation of the machine 
over a given area is to be avoided. 

59. A hand-tamping template and belt must be kept for use in case the 
tamping machine breaks down. 

60. (d) Longitudinal Floating.—Immediately after the screeding specified 
under IX (D) 56 (a) has been completed, the surface should be inspected 
for high or low spots and any needed corrections made by adding or remoy- 
ing concrete. Rough spots should be gone over with a long-handled float 
and worked to proper contour and grade. The entire surface shall then be 
floated longitudinally, with a float board not less than 16 ft. long and 8 in. 
wide. This float board shall have convenient plow handles at each end. 
It shall be operated by two men, one at each end, each man standing on a 
bridge spanning the pavement. The lower surface of the float board shall 
be placed upon the surface of the concrete with the long dimension parallel 
to the center line of the pavement. The float shall then be drawn back 
and forth in slow strokes about 2 ft. long, and advancing slowly from one 
side of the pavement to the other. The purpose of this operation is to 
produce a uniform, even surface on the concrete, free from transverse 
waves. The two bridges on which the workmen stand should be placed 
about 18 ft. apart when the length of the float is 16 ft. When the entire 
width of the pavement has been floated in this manner from one position 
of the bridges, they shall be moved ahead about 12 ft. so that the next 
section to be floated shall overlap the one previously so floated from 3 to 
4 ft. After this floating has been completed,-and all transverse waves 
eliminated, the surface shall be finished by the belting process specified in 
Paragraph 57. 

61. (e) Finishing at Joints and Tooling.—The contractor shall provid 
a suitable split float or split roller, having a slot to fit over expansion joints. 
This device shall be so arranged as to float the surface for a width of at least 
3 ft. on each side of the joint simultaneously. This device shall be used in 
such manner as to produce a true surface across the joint. Edges of the 
pavement, at joints and side, shall be tooled for a width of 2 in., the corners 
rounded to a radius of 14-in. 

62. (f) Trueness of Surface.—The finished surface of the pavement 
must conform to the grade, alignment, and contour shown on the plans. 
Just prior to the final finishing operation, the surface shall be tested with a 
light straightedge, 10 ft. in length, laid parallel to the center line of the 
pavement. Any deviation shall be immediately corrected. 


APPENDICES , oot 


63. The contractor shall be held responsible for the trueness of surface 
of the pavement, and shall be required to make good any deviation from 
the alignment, grade, and contour shown on the plans. 


X. CURING AND PROTECTION 


(A) Burlap Cover 


64. The contractor shall provide a sufficient amount of burlap or canvas 
for every mixer on the job, to cover all of the pavement laid in any one 
day’s maximum run. Burlap or canvas cover shall be made up in sheets 
12 ft. wide, and 4 ft. longer than the width of the pavement. Burlap or 
canvas cover shall be placed on the concrete immediately after the final 
belting, and shall then be sprayed with water in such a manner that the 
surface of the pavement will not be damaged. Burlap or canvas cover 
shall be kept continuously moist by spraying until the concrete has taken 
final set. 


(B) Wet Earth Cover 


65. As soon as it can be done without damaging the concrete, the surface 
of the pavement shall be covered with not less than 2 in. of earth, or 6 in. 
of hay or straw. This cover shall be kept continuously wet by spraying 
for 10 days after the concrete is laid. 


(C) Sprinkling or Ponding 


66. The sprinkling system of curing may be used if approved by the 
engineer. The sprinkling equipment shall be placed carefully, and without 
injuring the concrete surface. The sprinkling system shall be so arranged, 
and supplied with sufficient water at ample pressure, to keep every por- 
tion of the pavement surface continuously wet (both night and day) for 
10 days after laying the concrete. Dikes shall be constructed along both 
edges of the pavement, with cross-dikes where necessary, and the water 
flowing off the surface of the pavement shall be collected and led to the 
ditches or culverts as directed by the engineer. The contractor shall be 
held responsible for any damage to the roadway, shoulders, or adjacent 
property, by reason of escaping water. 

67. The ponding system of curing may be used at the option of the con- 
tractor. Dikes shall be built along both edges of the pavement, with cross- 
dikes at sufficiently frequent intervals, and the pavement flooded with 
sufficient water within the dikes to keep all portions of the pavement sur- 
face continuously covered with water for 10 days after the concrete is laid. 


(D) Cleaning 


68. After 14 days, the earth or other cover may be removed. After 30 
days, the contractor may use a mormon or a fresno scraper to remove the 
cover, except that scrapers shall not be used within 1 ft. of expansion joints. 
Cover within 1 ft. of expansion joints must be removed by hand. Road 


308 CONCRETE PRACTICE 


machines, or blade graders of the 2- or 4-wheel type shall not be used for 
removing the cover. 

69. After the cover has been removed, or ponds emptied and dikes 
removed, the entire surface of the pavement shall be swept clean and free 
from dirt and debris. Horse- or motor-drawn sweepers shall not be oper- 
ated on the pavement till 30 days have elapsed after the concrete is placed. 


(E) Cold Weather Protection 


70. Concrete shall not be mixed nor deposited when the temperature 
is below freezing, except under such conditions as the engineer may direct 
in writing. If, at any time during the progress of the work, the tempera- 
ture is, or in the opinion of the engineer, will, within 24 hr., drop to 38°F. 
the water and aggregates shall be heated, and precautions taken to protect 
the concrete from freezing until it is at least 10 days old. In no case shall 
concrete be deposited upon a frozen subgrade, nor shall frozen materials be 
used in the concrete. 


XI. PROHIBITION OF TRAFFIC 


(A) Barricades 


71. The contractor shall provide and maintain substantial barricades 
across the pavement, with suitable warning signs by day and by night, to 
prevent traffic of any kind upon the pavement before it is 21 days old, or 
before the cover has been removed. The contractor shall provide and 
maintain watchmen at each mixer, whenever the paving crew is not at 
work, who shall prevent destruction or removal of barricades, and keep 
traffic off the pavement. 

72. No section of pavement shall be opened to traffic until written instruc- 
tions have been given by the engineer. 


(B) Crossings 


73. At public highway and private crossings, the contractor shall pro- 
vide suitable structures to carry the traffic across the pavement without 
injury to the concrete. All such structures shall be subject to the approval 
of the engineer, and he may direct their improvement, or repair, as condi- 
tions may require. 


XII. CONDITION BEFORE ACCEPTANCE 


74. Before the road will be considered completed in accordance with 
these specifications, and acceptable to the engineer, the pavement, shoulders, 
ditches, back slopes, and structures, shall be placed in a neat and orderly 
condition, conforming to the plans and specifications in all respects. Equip- 
ment, surplus materials, and construction debris of every description shall 
be removed from the aoe of way. 


- APPENDICES d09 


TWO-COURSE PORTLAND CEMENT CONCRETE PAVEMENT 
FOR HIGHWAYS 


I. GENERAL 


1. It is the intent of these specifications to cover the requirements for 
the materials and construction of Portland Cement Concrete Highway 
Pavements composed of two layers of concrete made with unlike coarse 
aggregates, but of the same proportions. 


II. MATERIAL 
2. The requirements for 
(A) Cement, 
(B) Aggregates, 
(a) Fine aggregates, 
shall be as specified in Sec. II, (A), (B) and (a) one-course concrete highway 
pavement. 

3. (b) Coarse Aggregate for Bottom Course.—Structurally sound material 
considered too soft for a pavement surface may be used as the coarse aggre- 
gate in the bottom course. It shall consist of crushed rock, pebbles (gravel), 
air-cooled blast-burnace slag, chatts, or tailings. The particles of coarse 
aggregate shall be of clean, durable material, free from vegetable or other 
deleterious substances, and shall contain no flat or elongated pieces. 

(Note: In many cases it will be necessary for the engineer to specify the 
sizes, grading, and quality of coarse aggregate in accordance with local 
conditions. In every case, the engineer should provide specifications which 
will require the use of the best coarse aggregate, which is economically 
available. The following specifications covering size and grading of coarse 
aggregate will be found applicable in most sections of the country and are 
intended for use with proportions from 1:2:4 to 1:114:3.) 

4. The size of the coarse aggregate shall be such as to pass a 3-in. round 
opening. Coarse aggregate shall be uniformly graded within the limits 
shown in the following table, and any material which does not come within 
the limits specified shall be rejected. 

Passing 3-in. round opening, 100 per cent. 

Passing 2-in. round opening, not less than 82 per cent nor more than 95 


per cent. 
Passing 14-in. round opening, not less than 15 per cent nor more than 25 
per cent. 


Passing 14-in. sieve, not more than 5 per cent. 

5. (c) Coarse aggregate for top course shall consist of crushed rock, pebbles 
(gravel), air-cooled blast-furnace slag, chatts, or tailings. The particles of 
coarse aggregate shall be of clean, hard, tough, durable material, free from 
vegetable or other deleterious substances, and shall contain no soft or 
elongated pieces. The crushed rock shall wear not more than 6 per cent 
when subjected to the standard Deval abrasion test. When subjected to 
the abrasion test described on page 30, U. S. Department of Agriculture, 
Bulletin 555, pebbles shall show a loss of not more than 12 per cent. 


360 CONCRETE PRACTICE 


6. The size of the particles shall be such that at least 95 per cent shall 
pass a l-in. round opening and not more than 5 per cent shall pass a 14-in. 
sieve, with all the intermediate sizes retained. 

7. The requirements for 

Crushed rock, 

Pebbles (gravel), 

Air-cooled blast furnace slag, 

Chatts, or tailings, 

(d) Mixed aggregates, 
shall be as specified in Sec. II (B) one-course concrete highway pavement. 

8. The requirements for _ 

(C) Water, 

(D) Reinforcement, 

(EK) Joint filler, 

(F) Shoulders, 
shall be as specified in Sec. II, (C), (D), (E), (F), one-course concrete high- 
way pavement. 


III. SUBGRADE 
9. The requirements for subgrade shall be as specified in Sec. III, one- 
course concrete highway pavement. 
IV. FORMS 
10. The requirements for forms shall be as specified in Sec. IV, one-course 
concrete highway pavement. 
V. PAVEMENT SECTION 
11. Width and thickness of concrete pavement and the depth of the top 
and bottom courses shall be as shown on the plans for the improvement. 
VI. JOINTS 
12. The requirements for joints shall be as specified in Sec. VI, of one- 
course concrete highway pavement. 
VII. WATER SUPPLY 
13. The requirements for water supply shall be as specified in Sec. VII, 
of one-course concrete highway pavement. 
VIII. PROPORTIONING AND MIXING CONCRETE 


14. (a) Measuring Materials.—The method of measuring the materials 
for the concrete, including water, shall be such as to insure the required 
proportions of each of the materials as directed by these specifications. One 
sack of portland cement (94 lb. net) shall be considered 1 cu. ft. 

15. (b) Proportions.—The concrete in both the top and bottom course 
shall be proportioned 1 sack of portland cement, not morethan............ 
cu. ft. of fine aggregate, and not more than ............ cu. ft. of coarse 


S— 


APPENDICES 361 


aggregate. A cubic yard of concrete in place, measured between neat lines 
PIMEHCONTAIN his. ca barrels of portland cement. The engineer shall 
compare the calculated amount of cement required by these specifications 
with the amounts actually used in each section of concrete............ ft. 
long, or between successive transverse joints. If the amount of cement 
actually used in the pavement varies from the specified amount by more 
than 3 per cent for any section, the engineer may require the proportions 
of the concrete to be adjusted so as to use the specified amount of cement. 
If it is found that the amount of cement used in any section is 9214 per cent 
or less, of the specified quantity, the contractor shall be required to remove 
such section or sections, and replace them with concrete made in accordance 
with these specifications. Such removal and replacement shall be done at 
the expense of the contractor. 

16. The contractor may, at his option, construct the top course of mortar 
composed of cement and fine aggregate mixed in the proportion of 1 sack of 


CCS Pl 9 cu. ft. of fine aggregate. 
17. The requirements for 
(B) Mixing, ‘ 


(a) Operation of mixer, 

(b) Retempering, 

(c) Central mixing plants, 

(d) Consistency, 
shall be such as specified in Sec. VIII, (B), (a), (b), (c), (d), one-course 
concrete highway pavement. 


IX. PLACING CONCRETE AND REINFORCEMENT 


18. The requirements for 


‘(A) Inspection of Subgrade, 


shall be as specified in Sec. IX, (A), one-course concrete highway pavement. 


(B) Placing Reinforcement 


19. Steel fabric reinforcement of the size and weight shown on the plans 
shall be placed between the bottom and top courses, unless otherwise 
indicated. Fabric shall extend to within 2 in. of sides and ends of slabs. 
All laps of fabric sections shall be not less than the spacing of members in the 
direction lapped. Steel bar reinforcement shall be placed between the top 
and bottom courses unless otherwise indicated on the plans. Transverse 
bars shall extend to within 3 in. of the margins of the pavement. Bar 
reinforcement shall be placed and securely supported in correct position 
before any concrete is laid. All intersections of longitudinal and transverse 
bars shall be securely wired or clipped together to resist displacement during 
concreting operations. 


(C) Placing Concrete 


20. The mixed concrete shall be deposited rapidly on the subgrade to the 
required depth and for the entire width between longitudinal joints, without 


362 CONCRETE PRACTICE 


the use of intermediate forms or bulkheads between joints. While being 
placed, the concrete shall be vigorously sliced and spaded with suitable tools, 
to eliminate voids or honeycomb pockets. The concrete shall be especially 
well spaded and tamped adjacent to forms, bulkheads, and curbs. The 
bottom course shall be struck off at the correct elevation with a template or 
screed riding on the side forms. The top course shall be placed within 15 
min. after the bottom course was placed. Any dust, dirt, or foreign matter 
which collects on the surface of the bottom course shall be carefully removed 
before the top course is placed. 

21. Whenever, because of a breakdown or for any other reason, operations 
will be stopped for more than 30 min., a transverse joint shall be formed at 
the point directed by the engineer, to close the section. Both the top and 
bottom courses shall be completed to this joint. Any concrete in excess 
of that needed to complete a section, when work is stopped for morethan 
30 min., shall not be used in the pavement. 

22. The requirements for 


(D) Finishing 


shall be as specified in Sec. IX, (D), of specifications for one-course concrete 
highway pavement. 


X. CURING AND PROTECTION 


23. The requirements for curing and protection shall be as specified in 
Sec. X, of specifications for one-course concrete highway pavement. 


XI. PROHIBITION OF TRAFFIC 


24. The requirements for prohibition of traffic shall be as specified in Sec. 
XI, of specifications for one-course concrete highway pavement. 


XII. CONDITION BEFORE ACCEPTANCE 


25. The Condition before Acceptance shall be as specified in Sec. XII, of 
specifications for one-course concrete highway pavement. 


OS 


INDEX 


A 


Aggregates (See also Fine aggre- 
gates, Coarse aggregates, and 
Sand). 

definition, 1 
inspection, 188 
sampling, 188 
sieve analysis curves, 191 
tests of bulking effect of water, 
195 
colorimetric test, 194 
sieve analysis, 190 
silt in fine aggregate, 193 
standard method of test, organic 
impurities, 323 
sieve analysis, 320 
unit weights, 319 
tentative method of tests, de- 
cantation test, 322 
,unit weights, 189 
voids, 191 
Appendices, 303 
Aspdin, Joseph, 3 


B 


Basement (See Concrete basement). 

Bridges (See Reinforced concrete 
bridges). 

Briquettes, dimensions, 317 

molds, 317 

Buckets, drop bottom, 70 

Building units (See Concrete build- 
ing units). 

Buildings (See Reinforced concrete 
buildings). 


C 


Cement, 1 
(Also see Portland cement). 


Cement mortars (See Portland - 
cement mortars). 
tests (See Portland cement tests). 
Cementing materials, 2 
classification, 2 
Coarse aggregates, 12 
(Also see Aggregates). 
bulking effect of water, 14 
definition of, 1 
fineness modulus, 15 
inspection, 13 
kinds, 12 
sieve analysis, 15 
specific gravity, 14 
specifications, 15, 180 
unit weight, 14 
voids, 14 
Concrete (Portland cement con- 
_ crete), bonding new to old, 67 
consistency, 47 
tentative method of test for 
consistency, 329 
definition, 1 
depositing in forms, 66 
effect of various oils and liquids on 
concrete and protective treat- 
ment required, 339 
effect of various substances in 
concrete mixes, 23 
effect of various substances on 
hardened concrete, 25 
estimating, 154 
materials (See Aggregates). 
computing quantities, 49 
measuring, 48 
by volume, 48 
by weight, 49 
inundation method, 48 
tests required for, 212 


363 


364 


Concrete mixers, 55 
mixing, by hand, 51 
by machine, 55 
specifications for, 57 
placing during freezing weather, 
70 
placing under water, 69 
properties, 17 
abrasion, 22 
absorption, 22 
compressive strength, 17 
contraction, 22 
expansion, 22 
slump, 19 
unit weight, 22 
workability, 19 
proportioning, 26 
by arbitrary proportions, 28, 
199 
by Joint Committee table, 33, 
200, 324 
by sieve analysis and maximum 
density curve, 30 
by surface area method, 32 
by voids, 29 
by water-cement 
slump, 35, 202 
by water-cement ratio, slump, 
and fineness modulus, 38, 204 
general rules and theory, 26 
illustrative example, 43 
protection in freezing weather, 72 
protection while hardening, 68 
slump, 37 
test specimens—making and stor- 
ing in field, 335 
testing machines used, 213 
tests, consistency or slump, 198 
effect of age, 211 
effect of varying amount of 
mixing water, 205 
effect of varying fineness modu- 
lus, 207 _ 
required for concrete materials, 
219 
standard methods of making 
compressive tests, 330 


ratio and 


CONCRETE PRACTICE 


Concrete tests, tentative method of 
making consistency test, 329 
transportation, 61 
barrows, 61 
booms, 63 
buckets, 65 
carts, 61 
towers, 61 
waterproofing, by adding integral 
compounds, 74 
by proper proportioning, 73 
by water proof coatings and 
membranes, 75 
Concrete aggregates 
gates). 
Concrete arches (See Reinforced 
concrete arches). 
Concrete basement, concreting, 231 
estimating, 225 
excavation, 227 
forms, 229 
removal of forms, 232 
staking out, 223 
Concrete block (See Concrete build- 
ing units). 
Concrete brick (See Concrete build- 
ing units). 
Concrete bridges (See Reinforced 
concrete bridges). , 
Concrete building units, block, brick, 
and tile manufacture, 106, 298 
curing, 108 
dry tamp method, 107 
pressure method, 108 
- wet cast method, 108 
Concrete building units, block, brick, 
and tile specifications, 110, 342 
block walls, laying, 299 
pointing, 302 
Concrete culverts, 275 
concreting, 282 
estimating, 275 
excavation, 280 
forms, 281 
placing reinforcement, 281 
removing forms, 283 
specifications, 275 


(See Aggre- 


INDEX 


Concrete culverts, staking out, 280 
types, 275 
water area required, 276 
Concrete cylinder molds, 336 
Concrete floors, 271 
specifications, 272 
one course, 274 
two course, 273 
Concrete forms (See Forms). 
Concrete ornamental stone, 110 
Concrete pavements, 245 
crew organization, 252 
curing, 259 
design, 245 
estimating, 245 
forms, 251 
mixing, 255 
placing concrete, 255 
plant, 252 
proportions, 255 
specifications, 245 
standard specifications, 346 
one course pavement, 346 
two course pavement, 359 
subgrade, 251 
Concrete plant, 58 
for arched bridges, 297 
for paving, 252 
for slab and girder bridges, 292 
Concrete septic tanks, 263 
Concrete sidewalks, 233 
base, 234 
concreting, 236 
curing, 236 
estimating, 233 
finishing, 236 
forms, 234 
grade, 234 
location, 234 
specifications, 233 
Concrete steps, 267 
Concrete surface finish (See Surface 
finishing), 96, 101, 161 
estimating, 161 
granolithic, 102 
mechanical finishing, 96 
terrazo, 102 


365 


Concrete surface finish, wearing sur- 
face, 101 
Concrete tile (See Concrete building 
units). 
Concrete trim stone, 110 
Concrete wearing surfaces, 101 
granolithic, 102 
preparation, 101 
terrazo, 102 
Concrete window sills and lintels, 
269 
dimensions, 270 
forms, 270 
mix62 71 
reinforcement, 270 
Consistency of concrete, 46 
(See Concrete consistency). 
Contracts, 115 
definition, 115 
kinds, 115 
standard bridge contract, 116 
bond, 117 
contract, 119 
proposal, 120 
Culverts, 275 
(See Concrete culverts). 
Curbs and gutters, 241 
(See Concrete curbs and gutters). 


EK 


Estimating, 143-179 

building costs (square and cube 
methods), 166 

concrete basement, 225 

concrete culverts, 280 

concrete (materials, 
costs), 154 

concrete pavements, 245 

concrete sidewalks, 233 

concrete surface finish, 161 

excavation, 145 

forms, 151 

in general, 143 

miscellaneous items, 163 


labor and 


366 


Estimating miscellaneous items 
(block masonry, brick work, 
flooring, flashing, glass and 


glazing, heating, lighting, 
plastering, plumbing, roofing, 
sash, stucco) 

reinforcing steel, 158 

sample cost estimate, 172 

sample quantity estimate, 168 

Excavation, basement, 227 
culverts, 280 
estimating, 145 


F 


Field work, 218 
(For list of field jobs see table of 
contents). 
inspection of, 218 
supervision of, 220 
Fine aggregates (Also see Aggre- 
gates). 
definition, 1 
fineness modulus, 10 
general, 8 
sand, 8 
bulking effect of water, 9 
grading, 9 
Ottawa, 10 
sieve analysis, 10 
silt test, 9 
voids, 9 
screenings, 11 
specifications, 11, 129 
Fineness modulus (See also Aggre- 
gates, Fine aggregates and 
Coarse aggregates). 
of aggregates, 38 
of coarse aggregates, 15 
_ of fine aggregates, 10 
maximum practical values, 39 
Finishing concrete surfaces, 96 
(See Concrete surface finishing). 
Floors (See Concrete floors). 
Forms, depositing concrete in, 66 
estimating, 151 
for arch bridges, 293 
for basements, 229, 232 


CONCRETE PRACTICE 


Forms for buildings, 286 
for culverts, 281 
for girder bridges, 290 
for pavements, 251 
for septic tanks, 266 
for sidewalks, 234 
for slab bridges, 290 
for steps, 268 
for window sills and lintels, 270 
in general, 77 
metal, 91-95 
Blaw, 92 
Flore tyles, 95 
Floredomes, 95 
Metaforms, 93 
Meyer, 95 . 
steel craft, 92 
wall, 91 
removal of form marks, 96 
specifications, 134 
wooden, column forms, 88 
cost, 77 
erection, 79 
floor forms, 90 
lumber sizes, 78 
nails, 78 
removal of, 80 
rules for, 78 
ties, 83 
wall forms, 81 


G 


Gillmore needles, 316 
Girder bridges (See Reinforced con- 
crete bridges). 
Gravel, 13 
(See Aggregate and Coarse aggre- 
gate). 
Gypsum plaster, 2 


H 


Hand mixing of concrete, 51 
Hydraulic cement, 2 
Hydraulic lime, 2 


INDEX 


I 


Inspection of aggregates, 188 
concrete work, 218 
portland cement, 183 


L 


Laboratory (See Table of contents 
for list of laboratory jobs). 
methods, 180 
reports, 181 
work, 180 
Le Chatelier apparatus, 308 
Lime, 2 
Lintels, 269 
(See Concrete window sills and 
Lintels). 


M 


Machine mixing of concrete, 55 

Measuring concrete materials, 48 

Mixers, 55 a ie 

Mixing concrete (See Concrete). 

Mortars (See Portland cement mor- 
tars). 


N 
Natural cement, 2 


O 
Ottawa sand, 10 


B 


Parker, James, 3 
Pavements (See 
ments). 

Plans, 137 
abbreviations used, 138 
complete plans, 137 
reading plans and blueprints, 138 
standard plans for concrete high- 
way bridge, 139 


Concrete pave- 


367 


Plant (See Concrete plant). 
Plasters (gypsum), 2 
Portland cement, 3 
history, 3 
inspection, 183 
manufacture, 4 
dry process, 5 
quantity, 4 
raw materials, 4 
wet process, 5 
properties, 5 
fineness, 6 
set, 6 
soundness, 6 
specific gravity, 7 
strength, 6 
standard specifications, 303 
standard tests, 184, 303 
Portland cement concrete (See Con- 
crete). 
Portland cement mortars, 7 
properties, 8 
strength, 8 
weight, 8 
proportioning, 7 
tests, 196 
Progress charts and reports, 175 
Properties of concrete (See Concrete 
properties). 
Proportioning of concrete mixes 
(See Concrete proportioning). 
Puzzolanic cement, 2 


i, 


Roman cement, 3 
Reinforced concrete bridges, arches, 
293 . 
centering, 293 
forms, 293 
plant, 297 
pouring, 298 
Reinforced concrete bridges, slab 
and girder bridges, 283 
excavation, 283, 290 
forms, 286, 290 
foundations, 283 


368 


Reinforced concrete bridges, slaband Specifications, 


girder bridges, placing steel, 286 
planning construction, 283 
plans, 286 
plant, 292 
pouring, 288 
Reinforcing steel (estimating), 158 


S 
Sand (See Aggregates and fine aggre- 
gates). 
Ottawa, 10 


standard test for organic im- 
purities, 323 
tentative decantation test, 322 
Saylor, David O., 3 
Screenings, 11 
Septic tanks (See Concrete septic 
tanks), 263 
Sidewalks (See Concrete sidewalks). 
Sieve analysis (See Aggregates, Fine 
aggregates, Coarse aggregates 
and Sand). 
coarse aggregates, 15 
curves, 191 
fine aggregates, 10 
sand, 10 
test methods, 320 
Sieves (specifications and sizes), 321 
Slab bridges (See Reinforced con- 
crete bridges). 
Slag (See Aggregates and coarse 
aggregates). 
Slag cement, 2 
Slump of concrete, 37 
test, 47, 329 
test apparatus, 329 
Smeaton, John, 3 
Specifications, coarse aggregate, 15, 
130 
concrete brick, 344 
concrete building block and tile, 
342 
concrete curbs and gutters, 244 
concrete floors, 272 
concrete pavements, 245, 346 


CONCRETE PRACTICE 


concrete sidewalks, 
233 
detailed, 121 
fine aggregate, 11, 129 
forms, 134 
general, 120 
mixing concrete, 57 
proportions for concrete, 324 
reinforced concrete highway 
bridge, 122 
standard (See Appendices). 
concrete brick, 344 
concrete building block and tile, 
342 
method of test for making and 
storing concrete specimens, 
335 
making compressive tests of 
concrete, 330 
organic impurities in sand, 
323 
sieve analyses, 320 
unit weights of aggregates, 
319 
portland cement, 346 
surface finishing, 135 
tentative (See Appendices). 
method of test for consistency 
of concrete, 329 


decantation test for fine 
aggregates, 322 
Standard Ottawa sand, 10 
Steel forms (See Forms). 
Surface finishing (See Concrete 


surface finish). 
concrete floors, 271 
concrete pavements, 257 
concrete sidewalks, 236 
estimating; 161 
mechanical, 96 

rubbing, 99 

sand blast, 99 

sand float, 99 

scrubbing, 99 

tooling, 99 

washing, 99 
specifications, 135 


INDEX 


Surface finishing, use of colored 
aggregates, 100 
use of pigments, 100 


T 


Testing machines, 213 

Tests (See Various headings). 
required for concrete materials, 

212 
Time and work schedules, 173 
Transportation of concrete 
Concrete), 61 
Tremie, 69 


(See 


V 


Vicat apparatus, 311 
Voids in coarse aggregates, 14 
sand, 9 


369 
W 


Walls (rules for laying concrete, 
block walls), 299 
Water, bulking effect on sand, 9 
for concrete, 1, 16 
Water proofing concrete by adding 
integral compounds, 74 
applying water proof coatings and 
membranes, 75 
proper proportioning, 73 
Water-cement ratio (See Concrete) 
35, 38 
Wearing surfaces, 101 
(See Concrete wearing surfaces). 
Window sills, 269 
(See Concrete window sills and 
lintels). 
Wooden forms (See Forms). 
Work and time schedules, 173 
Work in the field (See Field work). 


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